I get what you're trying to do, I was just saying not all Amazon files have DRM. You didn't say if the couple of books you tried the quality check plugin (not sure if this works on all formats?) on were ones giving you DRM errors on the new device.
Not sure if the old DRM Check script would be of help here or not?
https://www.mobileread.com/forums/sho...d.php?t=121387
Any reason you're not just removing the DRM from all of your books so you don't have to deal with it ever again?