How does #3 square with Anthropic's literal warehouse full of books we've seen from the copyright case? Did OpenAI scan more books? Or did they take a shadier route of training on digital books despite copyright issues, but end up with a deeper library?

I have no idea, but I suspect there's a difference between using books to train an LLM and be able to reproduce text/writing styles, and being able to actually recall knowledge in said books.

I think they bought the books after they were caught that they pirated the books and lost that case (because they pirated, not because of copyright).