when dowgrading o world to a version between 1.8 and 1.12.2 while being on 1.13+, all the books becames protection while keeping their enchantments levels, giving us books with like protection 5 or multiple protections on one book, upgrading again does keep those books intact with the glitchs enchantements. Books obained with command to go above lvl 6 just became blank and when returning to a newer version, they rebecame what they were at start (like efficiency 6 go to blanck and then efficiency 6 again)