Exactly there was this study where they were trying to make LLM reproduce HP book word for word like giving first sentences and letting it cook.
Basically they managed with some tricks make 99% word for word - tricks were needed to bypass security measures that are there in place for exactly reason to stop people to retrieve training material.
This reminds me of https://en.wikipedia.org/wiki/Pierre_Menard,_Author_of_the_Q... :
> Borges's "review" describes Menard's efforts to go beyond a mere "translation" of Don Quixote by immersing himself so thoroughly in the work as to be able to actually "re-create" it, line for line, in the original 17th-century Spanish. Thus, Pierre Menard is often used to raise questions and discussion about the nature of authorship, appropriation, and interpretation.