I then altered the titles and covers of said books, and put them onto my Kindle. As per normal, I put some books into Calibre and the KFX plugin appeared to strip them of their DRM. To give some context, this venture started because I bought a new Kindle Oasis.

Thanks very much for your reply, and amazing work on your plugins - they've been very helpful. See 'Viewing books in KFX format' in the KFX Input documentation for ways to do that. You can also view the book after import to verify that it is readable. That is the easiest way to tell if something went wrong. If DRM removal fails you will be left with a book in KFX-ZIP format instead of KFX format. In addition calibre can make various alterations, such as downsizing images and regenerating the table of contents. Because KFX is not based on HTML, irreversible changes occur during conversion. Converting from KFX to KFX actually converts from KFX to EPUB, runs that through the calibre conversion pipeline, and then converts back to KFX.

Kindle kfx drm removal calibre