Unless they are very popular books, they will be weeded (thrown out or or sold) in a matter of a few years though. People imagine that libraries are infinite storehouses of material, but except for places like the Library of Congress they really aren't. There is limited storage space, and in order to get new books they need to discard the old ones that were rarely checked out. Even the example of old books on parchment aren't immune to this trend -- the books we have from Ancient Greece or Rome are just the really popular ones that were copied over and over again, and the vast majority of works from those times are lost.