LLMs compress data, there’s no way ChatGPT could remember every detail of the book alongside all the other information it stores in its encodings. The issue isn’t whether the entire text of the book is contained within the encodings, it’s whether it was trained on the book in the first place.
Here’s a good article about that: https://www.pcworld.com/article/394724/why-is-there-a-windows-11-if-windows-10-is-the-last-windows.html
Apparently that wasn’t really ever Microsoft’s official stance.