for what it's worth, i asked altman directly and he denied using libgen or books2, but also deferred to murati and her team on specifics. but the Q&A wasn't recorded and they haven't answered my follow-ups.
Unclear what that corpora might be, or if its the same books2 you are referring to.
books1 and books2 are OpenAI corpuses that have never (to my knowledge) had their content revealed.
books3 is public, developed outside of OpenAI and we know exactly what's in it.