I think you guys are confusing two separate things
1) The laws of magic apply to humans --- I do not think the White Council considers Denarians Human - at least while they are holding the coin.  Example - harry killed several with magic and no worries.   

2) The accords apply to supernatural nations.  the White Council has shown little interest in trying to enforce rules on other supernatural creatures so long as they leave White council members alone and do not rock the boat too badly.  The White Council has been in any number of wars with other supernatural nations.  The Accords does not prohibit this -- it just sets some rules to minimize the disruption that these wars cause to others non-combatants and minimizes the "total war" ethos of the combatants. 

This thread did make me realize we've seen a problem with the series so far.  I mean, Harry helped start the Paranet, what approximately 9 years/books ago now?  Sure, it took a few years to take off, but as off the last few books its going strong.

One of its main purposes was to identify upcoming people with talent and get them training, thus increasing the number of wizards and decreasing the number of sorcerers, right?  With the population the way it is, shouldn't we have seen some new apprentices taken on by wizards now thanks to the Paranet?

Yes and No. 

Yes - Paranet was set up.   Harry has certainly provided some training that is primarily defensive in nature (how to deal with supernatural threats) and it is certain that the paranet made ie easier for minor talents to find other minor talents who can provide some training as well as some collective protection. 

No - There has been no serious attempt by white council wizards to engage in any systemic training of minor talents in the paranet.  So it has been more "almost blind paranet elders teaching/leading the blind" type training.   Probably a few people have been identified/recruited to the white council because of involvement in the paranet, but no extensive testing or training or recruitment has happened.   White Council is focused on the war and its own internal conflicts.   

Molly was most likely the target of the so-called Black Council. Sandra Marling met her long before PG. She could have recognized her potential as a wizard and that her family connection placed her very well to act against the Knights of the Cross. The Knights are a target the BC acts against, it wasn't a complete coincidence that Michael was there in Grave Peril. Imagine Molly as an undiscovered warlock with her psychomancy fully developed on the side of the BC (Nemfected, maybe with a Coin). There lies the apocalypse.

Plausible and well thought out.  Does not feel right to me.   The knights are not about stopping outsiders, although they obviously can.  If you are right, this could be a side plot of the outsiders to distract the knights at the point where they want to finish the council.   Does not explain why the fetches were there though - and without the fetches the plot you described would not work. 

Mab and the Gatekeeper work more closely together than we knew at the time. I think they had the same information and maybe even decided together to share it with Harry, thus getting him on the playing field. The BC was up to something at that con in Chicago and it involved Black Magic. Nothing specific. Mab didn't know it was Molly at first or she could have done something more directly. Or get the GK to act, he is WC after all. Neither did she have plans to recruit her as a possible Winter Lady at that time. She didn't even know then that she would need one. And dragging her to Arctis Tor might have get her killed or her sanity ripped off her. Mab's first order of business was removing the prize from the hands of the BC, once she determined it was her (or Harry determined for her, he was the one who sent the Fetches right to the source of the black magic). Turning her into an asset instead in the long term by letting Harry take care of her: cherry on the top.

So the gatekeeper created the situation by hinting to Mab she investigate -- and Mab's investigation had the side effect of creating the situation.   Maybe.  But then you have all these high level players getting involved into something that is only important because all these high level players get involved.  It is a somewhat circular argument.

Do not get me wrong.  It may well be that there was some important reason for all these people to get involved, but all I am arguing is that nothing in the book identifies that reason.   All we got now is "important people are involved".

As to who fixed Little Chicago: I think it was the Gatekeeper. It would make sense for him to check on Harry, making sure he wasn't in on it either. He didn't fully trust Harry. His decision to send him the note might have been a test. If he observed him, he could have checked his apartment and lab for signs of suspicious activities. Little Chicago would have been interesting to him from a purely nerdy pov and he might have decided to not let Harry die from a stupid accident before he found out what was up with the young man.

As good an answer as anyone can provide.  Too little info here for me (at least) to have an informed opinion other than to exclude obvious "not" candidates

The idea that a lot of foreknowledge was required to set all of this up.

Molly was probably set up by Sandra Marling, who organized the con and met her at a shelter where she had to do community work. Sandra suggested to Molly that fear can cure drug addiction. There is room for a long-term plan here

.

Mab couldn't order Molly being killed, so she had to do something else in order to remove the potential danger a warlock daughter of a Fist of God would pose if she got recruited by the opposition. Hence the abduction. When Harry showed up to rescue Molly, Mab could be reasonably sure that he would take steps to turn Molly into an asset. Win-win.

The ideas above are possible (of course), but someone will have to explain what agenda people had here.  What agenda did Winter Queens have with Molly?   With the Con?  With Sending the Fetch into the mortal world.   Of course you can argue that Molly will be very important 5 years later and thus Molly’s involvement makes everything make sense (sorta not really), but Molly ascension to the Winter Lady is clearly a low probability outcome – and the future is probabilities.  It seems a lot of effort to for very low odds of having a maybe sorta kinda vague impact on a new winter lady.   Molly is related to one of the Knights of the Cross, but that is not Mab's concern even if Mab even knew about this.  And Mab would not help Uriel by killing a bunch of mortals in any case.    So again -- the actions of the Fetch do not make sense given what we know -- and foreknowledge or a plot against Molly (same diff) is a claim that does not seem very strong.   

I personally found PG a lot less confusing once I started to think about Mab's role differently. Harry is assuming she is a puppet-master who always knows exactly how things are going to play out in her favor. If you think of her as being in a corner instead and not knowing everything, her play makes more sense. She had to find out what was going on and who was moving against her.

This could be  real possibility -  but we just do not know what Mab's operation was trying to accomplish.  I doubt it had anything to do with the Con or Molly.  Ditto with Winter Mother's engagement.   

The long-term effects of this sequence: Harry's awareness of Nemesis, the sudden sowing of doubt among the Denarians, the beginning of the "Molly for Winter Lady" chain of events

ah - not seeing it.  Nemesis awareness was much later, doubt among Denarians is a good thing.  This story is the first where Molly begins her path as a wizard and that eventually leads to Winter Lady, but I have written already how unlikely (probability wise) that would have been.  Uriel arranging events to help Harry makes total sense -- he need to learn from Molly.  Molly as winter lady had to be a real long shot.  Uriel plays for long shots of course, but there are many many long shots.  You can just as easily argue that Molly could eventually have been the Merlin and had great influence over the white council.  Again - possible at the point of time where Proven Guilty occurred.   It is only later decisions that cut off that path.   

  I support Evil Bob as the one who fixed Little Chicago.  I suspect he is able to pass Harry's threshold, and can counter Harry's wards.

Have to go with others on this.  Makes no sense.  How would Evil Bob even know about Little Chicago.  Why would Evil Bob help Harry?  How could he do this when good Bob is ALWAYS in the room.      And there is no way he can cross Harry's threshold.  He was never invited and is a spirit.  He is a separate individual from skull Bob. 

The Winter Mother did it, Eldest fetch says so 'I have served the queen of air and darkness since before human memory.' but before human memory puts things in the realm of oblivion. Only 2 ways to do that is if original was still around in another form, or died. Either way he's talking about the queen possibly before it was ever part mortal.

Good logic - I like it. 

Not that it argues against Namshiel's presence (nothing says only one attacker used Hellfire), but I would note that Rosanna's absence from SG was also quite conspicuous. Also keep in mind Nic's comment in SmF about being sure one of the two women was "our own Judas".  Personally, my theory is Tessa is the ringleader for 1-3 traitor Denarians, but she's succeeded for the time being in framing Rosanna as far as Nic is concerned.

Quite possible.   Well thought out.    If you are correct, then we should see Tessa start to make her play soon after the events in Skin Game.  If that does not derange her mind and have the nemfection completely take over, not sure what would.   

All

I know it has been talked about before, but on many levels Proven Guilty does not make sense.  There seemed no reason for the Fetch to get involved and there are all these mysterious events at Arctus Tor.  Given this story is the prime candidate for the “time travel” experience of Harry, I wanted to poke at it.

Facts
•   “Darby” was booked a year in advance to attend the Con – by his lawyer
•   Madrigal (aka – Darby)’s lawyer/flunky was killed by the Fetch
•   Someone killed a bunch of Mab’s troll guards with Hellfire
•   Lilly and Maeve conspired to lure winter into leaving their borders to allow summer to attack the Red Court
•   Mab allowed Harry to recover Molly
•   A portal exists from the theater to Winter
•   The Fetch took Molly to Arctus Tor
•   Maeve slowed time in Winter so that winter armies would not threaten Summer for sufficient time -- such that Summer could attack the Red Court
•   The Red Court did a major attack on the White Council during the events in Proven Guilty – including targeting Luccio’s boot camp (ie – really important battle)
•   Somebody fixed Little Chicago (although this is more evidence of time travel than something relevant to the questions below)
•   Mab could NOT have sent the fetches to kill people at the con.  She is not allowed to do this due to the rules of Fey Queens.  Either someone else gave the command or the Fetches were killing on their own. 

Reasonably Certain
•   The Fetch killed the lawyer to shut him up because he knew things
•   The fetch knew enough about Molly to trick her into inviting them into the house (not a high threshold, but not complete ignorance)
•   The Fetch attacked the theater owner to keep the theater closed – presumably to allow them to feely use the portal
•   Madrigal was set up for some reason – somebody (- or something ) wanted him at the con
•   Molly did her first Black magic just days (or at most weeks) before the events in Proven Guilty – as she did not discover her friend was pregnant until then.
•   Nik was surprised (and very unhappy) to learn that Denarians were involved in the attack on Arctus Tor
•   The Fetch were involved because of orders from the Queen – but which one is unclear

Decent Guesses
•   Molly’s presence could not have easily been predicted without foreknowledge.  Not assuming foreknowledge as foreknowledge is a boring answer. 
•   The Fetch used the beacon that is Molly’s fear casting to enter the mortal world
•   Harry suggested Madrigal was set up to be the patsy to take the blame.  I would argue that Madrigal was set up to be the beacon.  But since Molly ended up being the beacon, Madrigal was thus unneeded.   
•   Thorned Namshiel was involved in the attack on Arctus Tor
•   Nik is afraid that a fallen is nemfected
•   Maeve might have been nemfected, but not so badly that her actions were highly influenced.
•   The Fetch were there for a reason beyond killing people at a con.  They are both spies and assassins after all.  Neither mission seemed to be relevant to what they did at the con. 


Questions
•   Which queen gave orders to the Fetches – or was the Fetch acting on their own?
•   If Madrigal was set up a year in advance, why.  I cannot have been related to Molly’s use of black magic or the battle with the Red Court as neither could have been reliably predicted a year in advance.    If he was set up from the begining, it had to be for another reason. 
•   Was the portal to winter always in the theater --- or did someone create the portal for this purpose?  The first might suggest a longer term plot while the second might suggest it was created by a Winter queen. 
•   Why did Mab not destroy those who killed her guards?
•   Did slowing time in Winter serve some other (less obvious) purpose?
•   When did Maeve and Lilly learn about the attack on the White Council?   Well in advance or only during the events in Proven Guilty? 
•   What else is going on that might justify time travel? 

Weighing in on the "you are what you eat" argument --- I am definitely on the "it will affect you".   Almost every instance of power granted has an impact on the personality of the person -- from winter power to using dark magic to breaking the laws of magic to fueling your power with anger to going vampire.   All that dark energy would totally turn Harry majorly dark.

But I think you are missing other very critical criteria that would make Dark Hallow Demonreach a problematic idea.
1) Gods are not humans.  No idea if the ritual would even work with non-humans.   
2) Gods are not humans.  Even if it could work, the gods are perfectly capable of guarding their power and NOT letting it be pulled out into the funnel.  If the power is not in the funnel, it cannot be part of the darkhallow.
3) Gods have mantles.  Not clear that mantles can transfer via darkhallow even if the individual (who is the god) could be killed and their native power absorbed by the darkhallow. 
3) You would have to let the prisoners out before they could be consumed by the darkhallow.  it would take these beings about 1 nanosecond to destroy harry, end the ritual and leave to destroy the world. 

The descriptions of the well, make it sound like it is capable of containing the coin collection. Especially with a warden with soul hire, and a pseudo nephlim spirit of intellect daughter.

I suspect it would be useless.  Oh I agree the well could contain the fallen angel.  But it would be pointless.  The coins represent an agreement between the angels and the fallen angels.  Imprisoning the coin in the well would not change that agreement.   A new fallen angel might be sent out to replace the imprisoned one.   

It can be argued that imprisoning the coin is a mortal decision and thus would be honored -- but I suspect there would be other consequences to balance the scale.   

I personally think balance requires the angelic forces to hold back more when a coin is imprisoned then when the fallen is actively working in the world.   This applies when a coin is held by the church or any other safe keeping.   However, when the coin is in the world actively tempting someone, that counts as fallen activity.  If this is true, then Harry having the coin for a few years without using it (despite temptation)  would then have been a good thing -- allowing angelic intervention without also allowing fallen evil to occur.   

The blessed cloths the Knights and Forthill cover captured coins in seem to prevent the other Denarians summoning a compatriot's coin back to them

The coins are all about choice.  That is why a fallen cannot just put a coin in your hand to corrupt you.  It does not work that way.   I suspect that choosing to give up the coin operates the same way in reverse.  It blocks the person from calling the coin.  I suspect the only people who "could" call the coin are people who choose to take a coin, but have not yet given it up.  Even other fallen could not summon a coin. 

As for sacrificing a Denarian, I think the only thing the Table would get is the personal, innate power of the Denarian.  The Coin is more like a weapon or a carried object, it probably makes no more sense to talk about sacrificing a Coin on the Table than it does to ask what would happen if you sacrificed Harry's .44 or Stallings' badge on the Table. 

The Denarian is the possessing spirit.  It has no blood to be spilled on the stone table.  The possessed mortal does have blood, but the fallen angel power is not imbued in that blood.  So quite doable, but not very useful assuming you can make it work in any case. 

Have to agree with Shift 8 that willful disbelief only gets you so far.  Enough witnesses and people change their mind even about the impossible.   Even assuming agencies/entities are pushing hard to discredit such witnesses is problematic given the scale of supernatural involvement with humans throughout history.  Even in Harry's personal encounters, he has met hundreds of people who "know something" and many of them are in groups (like SI cops or minor practitioners) where they know their peers have had similar experiences and it is safe to talk about what they see without being mocked or committed.   Multiply that by every city and  you get way too many people for disbelief to be something that "should" be effective. 

My personal guess is that something (spell/god/something) is actively encouraging disbelief to keep the mortals ignorant/complacent/unafraid.   Otherwise it does not make sense given how freely supernatural creatures interact with mortals.