"Resolved" = over (as in "story-ending").
These are advancements in their respective sub-plots & character-arcs.

I think  Michael's & Charity's are the only arcs we have seen "resolved."  Jim has said that retirement from the KotC job "is Michael's happily ever after."

I fully expect other "not fully resolved" elements to be introduced (or foregrounded) -- some to be resolved, some not -- before we reach the BAT (which, hopefully, will resolve most of the ones still open).

Lots of sub-plots and character arcs, but how much has the over all plot really advanced?  The important ones like who if any are on the other side that belong to the White Council? We've discovered a couple of cat's paws over the last dozen or so books, i.e. the Red Court and the Fomer or maybe they were the cat's paw of a cat who is the paw of a bigger cat, but as to just who they are is unknown..  We've known for sometime that Harry was star born, but have no clue as to what that means, especially for Harry.. We may finally find that out, or not...  We know that Mab is very important, and it is important that she have a sane competent Lady, we thought she had that once she killed her daughter off and got Molly... Well, no, when push comes to shove, she wants Molly killed... All these little sub plots are nice but mostly we don't know a lot more now than we did at the beginning of the series... When Harry became Winter Knight, yeah, lots of missions, cool, but have the politics of the Winter Court been explained yet? 

As I've said above -- I don't think the White X Winter alliance is the main point at all.  Sure, that's what Mab would have us think (and I expect she wouldn't object to having the Whampires in her service) but really now:  when Mab sets out a motivation, we should expect the another motivation behind that; and another behind that.

  I totally agree with all that you said, that's why I believe that Twelve Months maybe as significant as Changes.  Since Changes the story has sort of been treading water, or it seems that way maybe because the books since then have been so spread out. 

So, if Twelve Months is meant to be a book about changing things, one would have to work out what Jim is trying to change. Are we going back to a more familiar Harry? Or are we going to somewhere new?

 I think it will be a familiar Harry, but also different because now once he understands, he won't be able to escape who and what he is.  This understanding will color his character for the rest of the series, just as Battle Ground has changed the world's view of the supernatural for the rest of the series. 

   I don't know what to expect frankly.  Harry is grieving and from the few hints we do have from the short stories is suffering from depression, though maybe not on the level he was going through at the beginning of Summer Knight.  My prediction if you could call it that is, not just Harry, but both Lara and Molly will fight Mab on her plans for this marriage.  The real reasons why Mab wants it and their reasons for not wanting it, will make the story interesting.  It's a given that Eb will go postal upon hearing the news, but will he then step forward and attempt to do his Blackstaff duties?  Because I cannot imagine the White Council would be very happy upon hearing the news and if they really want to off Harry, they will try and get it done before he makes yet another powerful ally when he marries into the White Court.  And yes, I can see maybe two voices of sanity finally explaining to Harry what he is and what his birth means, those two voices belong to Rashid and Listens to Wind.

So thanks for bringing in the extracurricular evidence to back my theory 🙃 Harry's fire aspect changed because of how he used it. Intentions, even subconscious ones, color the magic used after all. An fire is directly related to sunlight aspect because it's all a flavor of summer as confirmed by hiding his blasting rod.
Maybe ask what a metaphorical man on fire is if you lack understanding of the concept off rip? Like hey, I didn't know that's the metaphor you gathered from Soul of the fire, Braveheart and other examples where the injustice of loss calls even the most broken men to war. Passion eh?

Capturing sunshine in his hanky and then not being able to duplicate the feat had nothing to do with how he used the sunshine.

Checked Reddit according to it, Harry told Murphy that he could no longer capture sunshine in his hanky or I imagine in anything else, because one has to be truly happyto be able to.  From the time that he lost Susan for the reasons stated until he had told Murphy that, Harry had never been truly happy so he couldn't do that feat again.  Now perhaps if he had tried it for the short time he and Murphy were truly together, he might have, if he tried, but we will never know because as far as we know, he didn't try.... But it's possible he did, because you never know when Harry might need a little sunshine in a future book.

so, after Susan was changed, an he unleashed his passion and outrage, he couldn't do the hanky? 🤔  most auspiciously what i said...
 

Passion and outrage had nothing to do with it, Harry had all those things, along with true happiness when he captured that sunbeam. Harry truly loved Susan, that made him profoundly happy, truly happy, a truly happy person can catch a sunbeam, it is as simple as that.. When Harry lost Susan that feeling of true happiness left him, capturing a sunbeam became impossible.

Honestly, I'm inclined to think not:  I think being Starborn is an Outsider-specific thing (and possibly a general ability to (eventually) overcome any/all mental domination)... but not a universal/overall powerup (I think   all.  that.  power.   is just Harry the Brute).  But the Rampires AFAIK never showed any Outsider-ish resistance to other WC wizards' magic (though that whole "Lords of Outer Night" is certainly evocative of some sort of relation to "Outsiders"), so I wouldn't expect the Starborn thing to give them any advantage.

I think there are hints in White Night, basically in what Lash tells Harry, page 363

"There was a complex confluence of events, of energies, of circumstances that would have given a child born under them the potential to wield power over Outsiders."

Harry goes on to say that Outsiders are all but immune to magic, and even a team of the most powerful wizards on the planet can barely slow them down.  Lash counters that Harry defeated one at the age of sixteen.

Then on the next page 364 Lash tells him;

"Listen," Lasciel said, giving my head a little shake. "You have the potential to hold great power over them.  You may be able to escape the power now held over you."

Basically the huge advantage that Outsiders have over humans and other creatures is their ability to put a mental whammy on them.  It screws everything up, including the massive power that say a wizard like Eb can throw around.  The main power Harry got as a star born in my opinion,  is that the Outsider mental whammy has no effect on him.. Or if it does, he has the ability to fight it off and turn around and attack the Outsider. It isn't about physical power levels or special spells, but Harry's mental toughness.. Yet another clue, what is Harry always talking about and taking pride in?  His will, he believes he can take on the baddest asses on the planet because his will enables him to do it.  Think about when he defeated HWWB when he was sixteen, it wasn't because of some spell he wielded or his raw power.  He defeated him because he withstood HWWB's efforts to scare and intimidate him.  That's not to say that Harry wasn't a very frightened kid, but he wasn't paralyzed by that fear.  Harry taunted him back, actually frustrating HWWB, then when he got to the gas pumps, Harry blew them up and HWWB along with them.

 I found the quote from Storm Front, page 65 hardback... The context is Harry has trapped Toot in a circle and Toot threatens if he doesn't turn him loose he will tell the Queen, presumably Mab, but at that point he could have been working for Titania.  Harry says he isn't afraid, Toot says he should at least pretend to be.. Then Harry replies that he doesn't have the time to be afraid.  That's when Toot goes into his tirade about time and people living now..  So here is what is said;
page 65 Storm Front

"Time,time," Toot complained.  "Is that all you mortals can ever think about?  Everyone's complaining about time!  The whole city rushes left and right screaming about being late and honking horns! You people used to have it right, you know."
I bore the lecture with good nature.  Toot could never keep his mind on the same subject long enough to be really trying in any case.
"Why, I remember the folk who lived here before you pale, wheesy guys came in,  And they never complained about ulcers or--" Toot's eyes wandered to the bread and honey again and glinted.

From the above I think it is pretty safe to assume that Toot was ranting about modern times and the people who live in modern times.. He was also talking about the Native Peoples that lived on the continent before Europeans arrived.  Though when you think about it, it doesn't matter if Toot was talking about ancient Celts of Europe or Native Peoples of the American Continent, he was referring to modern people verses ancient.  I think it was a throw away rant in a lot of ways, but it also gives us some insight into who Toot is.  In other words he might be tiny, but by his own lights he isn't stupid and should never be underestimated.  This in many ways sets the tone between Harry and the Wee Folk, Harry understands and respects those facts about them, thus is able to work with them and gain their loyalty where others have not.