Comment by suspended_state

Disclaimer: I am not a lawyer, this is just my interpretation of the situation from the comments above.

I don't have an answer to your question, which seems more general and doesn't correspond to the situation described by the article anyway: here the corporations have the right to use copyrighted materials to train their model, in the same way that you are allowed to learn from the same materials. You might even learn it by heart if you want to, but copyright laws forbid you from reproducing it, and in this instance the Japanese law tries to follow the same principle for AI models.

How should the corporations implement their training to prevent their models to reproduce the material verbatim is their problem, not the copyright holder's, in exactly the same fashion if you learn an article by heart, it's on you to make sure you won't recite it to the public.