The books carry a release date. It doesn't always move when the text does — so this checks every book daily and publishes what changed, announced or not.
Each book is downloaded daily, its text extracted and hashed, and compared against the last copy stored. Nothing is flagged unless that hash moves — that part is arithmetic, not judgement.
When a book does change, the exact difference is worked out automatically, Claude writes a plain-English summary of it, and this page updates on its own. The raw diff is published beneath every summary, so if a summary gets something wrong you can catch it. Don't take its word for anything that matters — check the diff, and the book titles above link straight to the source.