A bit that's forgotten by everyone (EXCEPT ME, I WILL BE VINDICATED) is the Lost Book in Small Favor.
In SF, Harry goes looking for a book on the Fae in his office, looking for information on gruffs. But... it's not there. Instead, there's a book of Calvin and Hobbes comics.
This is insane. Harry A) is a book nerd B) Has a well-organized library C) Has Bob to remember where all his books are and D) Has such a small social circle that no one could have easily taken it.
Whoever the time traveler is, "borrowed" that book. Harry makes the most sense by far.
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Also- I strongly, STRONGLY doubt that Mab fixed Little Chicago without any time travel schenanigans going on. Not only would that be an incredibly unsatisfying conclusion, it also makes no sense that it would have been a secret for so long.
Not to say that Mab doesn't keep secrets- just that this one would be pointless and boring.