Some people say yes, some say no.
Personally, I think that knowledge lost is simply lost. It makes it so much more valuable for one & balances the game.
I've come to accept that since the Guernicus have rituals that can look into the past, one could use those & re-copy the book.
Basically, if the book was of sufficiant importance that the balance of the Order was in Jeopardy, a Quaesitorial investivation would be lunched & a copy of the book would evantually be found.
Books found in an old library that are dammaged by time or burned in a fire could also be re-copied using the mighthy Time Rituals but since their value is not established, they probably will remain in their lost state for a long long time.
Healing spells could restore the physical part book but the knowledge has been lost to Time.
In a viable setting I could see an ancient artifact in Alexandria's great library that allows you to read the dammaged text if a copy of it was ever part of the Great Library. Simply bring the dammaged tome, place it on the Magical desk & the Knowledge is restored so long as it remains on the desk.
W