I like the idea that Demonreach is Avalon, and is Atlantis, and... other similar myths... it's a VERY Dresden Files thing to do...

Theory 1: I think the coins are meant to circulate, Nick could very well be using Andurial to find them and get them out... but I think that is at best shortening the time they are held for, and usually not by much. If this were the primary method of them getting out then Nick would have far more of them and the other Denarians wouldn't have so many... but we see Nicks wife with a stash too, I think they just get out, I think the fallen bend fate from inside the coins to get out... 1 in a million chances happen and someone touches one on accident... maybe without realizing it...

Most Knights are called for one event and stop serving (like Susan or Karen at chicken pizza) who is to say that most Denarians don't do the same... possibly with a mind wipe to forget they ever took up a coin or possibly never actually took up the coin, just got a shadow that took them... Nick tries to have Lash disable Harry when he knows Harry hasn't taken up the coin, so we know the shadows can do that at least.

Theory 2:

My bet is on Sarissa, her mother was a magic user and she is a Changeling, she could easily have had wizard level powers suppressed by something not unlike a nicer version of thorn manacles, or set them aside before meeting Harry in Cold Days and Nameless a member of the Winter Court was an associate of Kemmler, and would be able to teach all sorts of dark healing. He is my suspect for Cowl.

The one character who we KNOW has found someone who was Nemfected, found not one but TWO Nemfected individuals... I doubt Mab would miss the fact that Sarissa was Nemfected, and if she suspected Nameless of Nemfection she would deal with him... I don't think any theory that requires Mab miss Nemfection in someone close to her (and Sarissa is) is a great theory...

Kim Delaney is a reasonable guess for Kumori... not going to totally throw in on it, but reasonable guess... I approve.

Theory 3:

Theory 3 ignores the Peace Talk/Battle Ground split The Novella The Law and the additional bookTwelve  Months which all bugger up the number order, besides Cowl and Kumori appear in Grave Peril and are quite clearly driving the events to nemfected Lea, set up the Red Court War etc. The pattern is I think is that Cowl is directly or indirectly in every case file, where he isn’t responsible for the A Story he is responsible for the B Story.

Agreed, also Dead Beat and Proven Guilty were swapped due to book 7 being the first Hardback... though who is to say which portions of Dead Beat were moved to Proven Guilty and visa versa... Nick shows up every 5 books (book 5, 10, 15...) and a word of Jim saying he will 'show up on schedule' before book 15... so there is something to the idea of X shows up every Y books but some of that was messed up with the swap of 7 and 8 and more of it with the split of 16, the swapping of 17 and 18 (Mirror Mirror and the Wrestling book were swapped around the time Peace Talks came out) and the insertion of twelve months...

So what was 16, 17, 18 became 16, BG, TM, 18, 17 and that pushes out the last of the case files too... so even Nick (the one clockwork thread we KNOW is true) may not be on schedule anymore.

Men change a lot after 16... I think that is all he was when he fought Justin. though Justin is dead and I think Cowl is male. Eb's seen him repeatedly over the years, though, and will have a better eye.

Harry is one of if not the strongest wizards of his generation, Justin was aware of that, I don't see Justin making that comment even if he was alive.

I got the implication that it wasn't a secret... The Nations of the unseelie accords voted to declare war and created the Ministry, that wasn't done in secret (I mean, they didn't include non-magic mortals, but within the magical community it wasn't done in secret).  The Ministry then met in closed session behind veils.  I don't believe this meeting itself was a secret any more than when the US Congress meets in closed session is a secret... everyone knows they are meeting they just can't watch or participate.  Even if the location was a secret my guess is that Harry can find Mab if he needs to through winter unless she specifically shields that connection.  No one seems surprised that Harry showed up (Gard for example just accepts that he is there and while she draws on him she also listens to him without freaking out that he knows about the meeting.)

In Christmas Eve we find out that Maggie came home from her first semester of school with a GPA 'above 4.0'... Maggie is in Elementary School (my math says 5th grade).

GPA is out of 4, the highest you can get is 4, straight A's is a 4.0.

In Highschool if you take AP courses you get +1 point per AP course (so an A is 5.0) making it possible for a HIGH SCHOOL student to get higher than a 4.0.  A Junior High School student would need to take a high school level AP course to get higher than a 4.0, an Elementary School student would not be able to get a 4.0. Period.

Goof? or did Maggie skip grades? (Skipping grades (three of them?) AND taking AP classes and getting straight A's and doing all that after immigrating from South America to Chicago and growing up without parents and...)

This is just a mistake by Butcher right?

I don't think that quote kills everyone from his past. Someone might have been out of touch with Harry, and wondering if he missed something. Maybe some wizards are late bloomers, and develop power later.

I agree, it doesn't kill everyone from his past, just people who knew him well while he had magic like Justin or Elane or Eb... really just those character from the ones we know.  All of those know Harry is strong and wouldn't be interested in facing him in combat just to see how strong...

Harry wasn't a late bloomer and as far as we know Justin didn't show him off to anyone, so there shouldn't be anyone else from his past, though Morgan was watching him before Malcom died and Justin got him, so someone else may have been at that point too and they wouldn't know how strong he is...

When the Archive dies the construct passes to her daughter and the construct was built with a protective instinct, the host will avoid danger and bias towards protecting herself... So, what happens if the Archive dies without offspring?

Will the construct unravel?
Will the construct pass to the eldest descendant of the prior archive (cascading back as needed)?
Will the construct pass to the nearest compatible vessel (as the mantle of the winter lady does) say a random librarian?

Can an archive adopt a daughter to create a safeguard or does it have to be a natural daughter? Can the construct pass through a male (Say an archive has a son, who grows up and has a daughter, can that granddaughter inherit if the archive has no living daughters?)