[tab][/tab]We never had such a book. What we do have is minor mentions in the "Catalogue of Magical Beasts and Beings", specifically the commentary written by Antonio Perez of Flambeau, former Pontifex, who made specific comments about local beasties in Andorra. There, in descriptions of a few beings, he will make mention of the caves and past explorations, in the context of "such and such a being was encountered, it looked like this and talked like that, was some sort of what, and it did/done/acted however".
[tab][/tab]Another good place to research is in the covenant records. You are correct in the oversight that there is no copy of the covenant records in the library. This is because this is not where they are kept. They are in the Records Room, adjacent to the council chamber. It is fair to accuse me of making that up just now. But I made passing mention of it once long ago I think. Maybe. There are rules in Covenants (I think) where it says so many years worth of records is equal to a tractatus on Area Lore of the covenant.
[tab][/tab]A third place to research is more difficult, but not impossible. When Carmen inherited her father's old sanctum, she also inherited his personal journals (last used as a McGuffin in the Winter Drake Hunt of Winter 1230.
[tab][/tab]And finally, there does exist a book written by Xagygyrag of Bonisagus. It was submitted to Durenmar a long time ago.