Comment by jsheard

This dataset includes "books3", which is a comprehensive dump of Bibliotik, a torrent tracker dedicated to pirated ebooks.

Throw a dart at a wall filled with every notable author/publisher ever and whoever you hit probably owns some of this data.

Apparently you can just do whatever as long as you say it's for AI research, go post Blu-ray rips online, it's fine provided you have a .ai domain :^)