Well you would not really be overlapping them as they would be on separate geometry. You would have a separate set of uvs for each book. They would simply be on top of each other in your scene and the renderer would handle not drawing the sections that are on top of each other.

Imaging what would happen later if you wanted to add a third book or change the angle the two books are on top of each other or have a character pick one book up. You could not do the last one, and you'd have to remodel your combined book stack for every other change.

Better to model all the books as separate objects.