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.