The bug

When you load a 1.8 world in 1.13 book names disappear and the book says Invalid book tag. This is obviously a problem, especially if there's books in old chunks that haven't been loaded forever. Case in point: https://mcworldmap.com/worlds/eTbLl. On the bright side if you load all the chunks in 1.12 before 1.13 the world smiles at you instead and lets your innocent books live.