David, thanks for such a detailed reply and the user partition suggestion. That one would be everything visible on the mounted drive and nothing else, correct?
I basically want to keep the accumulated stats (total number of books, hours) and Reading Life awards. I only read one book at a time, so I'm perfectly happy to do it in-between books. But if backing up the whole user partition is a sound approach then maybe I'm over-engineering the solution to the problem
I've already deleted the kepubs from the library. I downloaded and sideloaded the epub versions of those books I bought, so I didn't need the kepubs coming back after every sync