Also, a lot of that sort of stuff likely is not written down! Who is writing down the wards and tricks to their castle - if anyone finds it, they may be able to thwart your defenses! Or reverse engineer them.
Almost everyone would write things down during the planning-it-out phase. You may destroy the notes, but
making them up-front looks nigh-inevitable.
Denarians have the mental capacity to just know things -- Angels I think have something like
intellectus for their domain. And they know enough not to commit critical plans to any form of writing. Odin likely, too; and Ferrovax & the other dragons.
Mab... maybe. I think the Archive was a deep secret from before Mab was Mab... even before she was born a mortal girl.
The Nickelheads may have a lot written about them. Possibly a WHOLE lot. And much may be contradictory - we do not know she can sort out true from false, just she knows what is reported.
I'm pretty sure the Archive has an absolutely superhuman ability to sort information, correlate and organize it. Denarians are likely the only entities capable of perpetrating a deception upon the Archive, and even THEY will be challenged -- they don't know what other info may be out there, with dangling threads the Archive can tug upon to unravel their lies.
Who would write down much about his Mom? Maybe Eb, but that is likely it.
The Wardens, to begin with. Harry had seen Warden reports on Hannah Ascher, recognized her on sight. Morgan kept a journal, and I doubt he was the only one: wizards live for centuries, and being able to remind yourself of details from long in your past could be crucial. Eb has a huge set of books from the magical master/apprentice lineage of Merlin. Wizards
love books & writing!
The Whamps, for another. Lara confirms that House Raith has profiles on most of the Wardens themselves, and I presume they have similar profiles for other "interesting" humans (and other entities, too!). And we
know House Raith thought Margaret LeFay was interesting!
It wouldn't surprise me if the Ramps had kept such records, either.