Are there any "text caches" that we still are not sure what's inside?
Are there any "text caches" that we still are not sure what's inside?

Petrarch - Wikipedia

In 1345 he personally discovered a collection of Cicero's letters not previously known to have existed, the collection Epistulae ad Atticum, in the Chapter Library (Biblioteca Capitolare) of Verona Cathedral
So basically a guy goes into a library, rummages for a while, and finds ~1400 years old text no one knew was there
Do we still have places that store texts (like libraries, but doesn't have to strictly be a library) where we don't have everything catalogued and we don't know what might be inside?
I would assume that almost any old library or private collection that includes old handwritten books has at least a couple of manuscripts that nobody has read in decades if not centuries.
A few years ago, a researcher started going through a large stack of dusty old music manuscripts in an east European archive, and discovered an unknown work by Stravinsky, over 100 years old. I wonder what was in the rest of rhe stack.
Huh, that's an example of what I've been looking for
What phrase should I search for to learn more about the archive?
But do we know if those have been generally indexed?
In proper libraries, we probably have the author and title in a database somewhere but not the content. In private collections, all bets are off.