There is a tool that used to provide cover thumbnails for azw3 personal documents (the ones that are affected) but has ceased to work with one of the later firmwares. Last time I checked, the creation of apnx files (which store “real” page numbers) was still functional.
In short, this application will give you generic “real” page numbers for pdocs that were sent to your Kindle wirelessly.
You can find it here:
https://github.com/quiris11/ExtractCoverThumbs/releases