My understanding is a lot of those were just wrappers for mobi files to add even more drm, but I haven’t looked super closely.

I dunno. I used to be super hardcore about ripping every book and putting it in my calibre library. Then I eventually realized that… mostly I don’t care. There are very few books I am going to re-read and the majority of those were so good that I either want the hardcover to put on a shelf or don’t mind buying again from a vendor that gives the author a better percentage.