How exactly can Harry rule out a different necromancer going there since he left ?

Maybe he can't, but why would another go there and also use necromancy?

Oh, wow.
I didn't even look at the part of the scene where Harry adds the coin from the drowned guy and one of the Kincaid-killed-them guys, without altering the final coin-count at all.
Yeah, I'm not trying to rationalize this anymore. I'm just going to with my good friend Occam, throw my hands up in the air, and ask the Mighty Jim why he does this to me. 
He's so... not detail-oriented. It makes everything so stressful for those of us who make lists and are kinda OCD and tend to over-analyze wayyy too much. It's almost like he's just focusing on the story and plot and characters and silly things like that rather than the miniscule details that almost nobody actually ever catches until read-throughs or even really care about anyway because in all probability they completely lack any actual relevence.
*Sigh.*

I feel you Ziggelly. It makes me paranoid to even try to come up with theories that may be plausible depending solely on whether or not a piece of info is an actual goof or an intentional discrepancy. Thus, Jim sows his tales as we reap epileptic trees.

You didn't read the Harry Potter books, did you? 

What I'm proposing is that Harry be sent back in time by GK to learn more about the Black Council, nothing else.  Of course, then he ends up playing a role that he didn't know he would. 

For example, Future GK helps send him back specifically to NOT change the past and only observe the BC shenanigans.  And one of the first things he does is accidently bump into PG GK.  PG GK realizes he's from the Future, and threatens to punish him for breaking a law.  Future Harry manages to convince/prove to PG GK that he traveled with Future GK's help and consent.  PG GK lets him go, and as he's departing, Future Harry makes an off-the-cuff comment about giving him a little more detail this time when he warns him about the black magic stuff.  PG GK says, "um, I have no idea what you're talking about".  And Future Harry says "yeah, you tell me there's dark magic being performed in town, and you have me look into it."  To which PG GK says, "First I heard of it."  Which confuses Harry, until he begins to realize that he sets that in motion.  Which then has him worrying about what else he may have already set in motion the first time, but doesn't know what he has to do this time around.  Queue internal dialogue rant about making things difficult for himself.

Thus Harry has to balance not changing anything other than what needs to be changed to match the first time around, while also trying to investigate and learn more about the BC.

No, time travel isn't needed to make it work.  But time travel could be used to explain things in the book that went unexplained which his theory didn't touch on, and could also be the way that Harry finds out about the plot which Knnn spelled out.

I don't think Harry Potter did it well, but it had way more plot holes and inconsistencies as a series than TDF does. Time travel also introduced critical logic issues into that series. Information and items don't just appear out of nowhere.
(see: http://en.wikipedia.org/wiki/Predestination_paradox and http://en.wikipedia.org/wiki/Bootstrap_paradox)

Besides, who says the bad guys are doing it constantly and that there aren't good guys who have had to travel back to "fix" things themselves? For example, I think the instance in which Harry "was supposed to die" at the hands of Corpsetaker could have originally played out that way, but was altered by someone traveling back and alerting Marcone. Harry would not have been able to do that (in this particular instance), so it strikes me that perhaps there are have been several alterations to the time stream, but that we only see the the altered time and not the original situation that had to be "fixed."

You'll have to forgive me I didn't read all the comments so I hope I am not repeating something.

Serack, some questions for you if you can answer them.

Do you think Fitz will be able to control the change (or be trained to control it) or have his human consciousness afterward? 
Does he have a soul or some mixed hybrid of one?
Would this explain why he was able to hear Harry?

Sure, I'm not Serack. But I think I can address some of your questions.
Wolves are all over mythology for several cultures -  sometimes good, sometimes evil. In many cases, especially that of Native American lore, they are somehow linked to the supernatural. Based on Jim's use of mythology and folklorem I think Fitz's ability to perceive things beyond the natural world could be attributed to his wolf heritage (should he turn out to be Tera's son).

FM - Meets the Alphas and Tera West
SK - Gains Mouse
DM - Is given custodianship of Fidelacchius
WK - Establishes Paranet
SF - Is given custodianship of Amoracchius

Oh and here's an unsolved mystery to add to the list:

Who is Victor Sells?

We never really find out who he is really, other than his wife stating that he was not speaking to his family (to her knowledge), nor did he really speak about them with her. Perhaps he has an as-yet-to-be-revealed insidious background?

Interesting, thanks for posting that. Although it doesn't say "any" enchantment, so that might give us an out for Luccio's failure to act....

For that matter, if they could actually unravel ANY enchantment -- as that unravelling cloth did in Summer Knight -- then they should be able to "cure" things like the half-turned Red Court vamps. And we know they can't do that, or Harry would've gotten somebody to lay them on Susan already (or something similar). So that makes me think that there are limits to the enchantments they can affect...

Maybe it's more along the lines of spells/wards and not necessarily objects/creatures that are magical in nature.