After an interruption, I've continued with my Nicolai browsing, and volume 6 contains several jewels. cahn, there are a lot of Quanz stories, including the one which made it into many a fiction, of FW nearly surprising Fritz and Quanz playing the flute, when in comes Katte to warn them, and Quanz hiding just in time, but also one from Fritz' time as King, which is very Fritzian. Background: Quanz only said "Bravo" when Fritz' play was good enough (though otoh he did not, Nicolai emphatically says, say "rubbish" or grimace when it was bad, he just withheld the applause). The anecdote goes thusly: Quanz makes a new flute for Fritz, Fritz plays but makes mistakes, promptly blames the flute, Quanz checks the flute again and says no, the flute is good, Fritz says it's not true and shouts, they don't talk for a week during which Quanz withholds applause and approval, after eight days, Fritz caves and says okay, yes, it was him, not the flute, Quanz is "okay, then let's practice". Also, Quanz - whom Nicolai knew, and who is his source for all these stories, once said ruefully about Fritz as a person and why despite their ups and downs he can't bring himself to leave him, that he'd miss him if he left: Ich hätte nicht gedacht,dass mir der Mensch so nötig wäre. ("I wouldn't have thought that I need this man so much.")

mildred_of_midgard, apparently until the early 1790s, the most common spread story about the escape attempt was that Fritz and Katte were both arrested at the same time, at Wesel. Nicolai corrects this and says he's had it from a son of a former Gens d'Armes comrade of Katte's that Katte was in Berlin, and that the plan had been for Katte to escape separately, and then tells the "you're still here?" story that subsequently is told everywhere else. There's one detail that I haven't seen in later versions, and that is that when Katte is moved form his original arrest place, the officer in charge of the transport is optimistic that he'll be released once it's all cleared up, and Katte replies "Non, mon ami, le tyran demande du sang". I can see why this story didn't make it into other accounts, though, because unlike Nicolai, we've seen the interrogation protocols and Katte's petitions for his life etc., and I don't think it occured to Katte this early that the death penalty (as opposed to imprisonment and possibly physical punishment) was where this was going. Still, I thought you'd like the quote.

Nicolai's version is also the one where Peter gets the "sauvez-vous" warning note from Fritz and therefore hightails it out of Wesel, which was we now doesn't work, date wise. He (N) says his source isn't sure whether Peter then initially took refuge with the French or English ambassador in Holland (we know it was with the Brits, but with Chesterfield's staff rather than Chesterfield himself), and has him directly interact with the unnamed envoy, but the trajectory of Peter's flight otherwise is correct, as is Peter's later career, and Nicolai says his source's dad knew Peter personally as well. This supposed former comrade of Katte's and friend of Peter's whose son is Nicolai's source is called von Hertefeld.

Aaand then I saw Nicolai has yet another version of the Glasow story in the offering, which is far too good not to give you verbatim, which I shall do in another comment (it's that long).