Rex Stout’s Nero Wolfe mystery novels take this angle, with narrator Archie Goodwin ‘writing’ the books, a fact he mentions a few times throughout the seventy some-odd tales (between novels and novellas). It’s highly successful because unlike the Holmes/Waltson dynamic, Archie admires but isn’t in awe of the great detective whose tales he’s chronicling, and in fact I’d say Archie is at least 50% the protagonist versus Watson’s nature as an observer (albeit an involved one) to Holmes’s genius.
Archie’s pretty snarky about Wolfe’s foibles, which is refreshing. I don’t recall him ever mentioning whether Wolfe himself read the books–but knowing Archie, he wouldn’t write any more deferentially if he knew Wolfe would be reading. (Actually, I’m now remembering something about Archie giving Wolfe a compliment and writing as an aside something like, “I won’t say any more just in case he reads this; his head is fat enough.”)
Sometimes he mentions getting letters from people who read the narratives, and now and then later clients (I’m thinking of their original client in Prisoner’s Base in particular) reveal how thrilled they are to see the famous office Archie’s described in the books.
He also has a couple of forewards, depending on the circumstances, where he issues a disclaimer. In The Black Mountain, “Archie” warns that in many ways, this book is a phony, because so much of it took place within Montenegro, with dialogue taking place in a language Archie doesn’t speak. So he had to get it translated by either Wolfe or a language course.
Another method he uses is at the end of a couple of cases, implying that he might not publish the book at all depending on certain events. Something like, “The case is still pending and for all I know, this may never see print. If you’re reading it, s/he was found guilty. If not, it’s been stuck in a drawer and that’ll be the end to it.”
Archie makes an unreliable narrator to some extent, because very rarely–to maintain suspense–he keeps certain assignments from Wolfe a secret, or at least fairly obscure, until they’re already in play (now I’m thinking of The Doorbell Rang, my personal favorite of the corpus). Other times, he cheerfully admits leaving some more realistic (i.e. cursing) dialogue out because a middle-aged schoolteacher in the midwest “might read this and chastize me” (or words to that effect).
Anyhoo, that’s how things stand in the Wolfe series.
Another epistolary novel would be Les Liaisons Dangereuses, fairly famously told via letters. I’m trying to decide whether the Edmund Crispin mysteries starring Oxford professor/genius Gervase Fen would count in this. It’s difficult because they might simply be fourth-wall breaking. Fen seems to either be a) fully aware that he’s having his events chronicled by the author, or more surreally b) conscious that he’s a character in a book.
I use as an example his exploits in The Moving Toyshop. One scene has Fen and a new friend (the book’s primary POV character) attacked and knocked out for a while. When the POV character wakes up, he hears Fen reciting things like “The Blood on the Mortarboard, Fen Strikes Back, A Don for Death…” After a while, the friend asks groggily what the hell Fen is talking about. Fen says in his usual insouciant way that he’s been spending his time “thinking up titles for Crispin.” So he knows his exploits will be recounted by author Edmund Crispin; it’s not clear whether this is because he’s aware he’s fictional, or whether Crispin is just his writing agent/publisher.
It’s a great series, by the way. Very charming, especially if you enjoy that kind of meta humor.