The case by case basis was about acquisition and possession of the copyrighted material. Anthropic pirated a large number of books and illegally stored digital copies of many that they did purchase legally. The training being protected doesn't give them the right to violate copyright in that way.
Google, for example, purchased print versions of their training material and had a small army of employees digitize them and then delete the digital copies when they were done. That hasn't been challenged AFAIK, but would likely have been found to be not a violation. That's I think what was meant by case by case basis.
It's like if someone breaks into my house and I shoot them with my gun, that's very likely self defense, but if I'm not allowed to own a gun, I may still end up in trouble with the law.