Are you having the same problem as in this thread?
https://www.mobileread.com/forums/sho...d.php?t=262285
(I don't think so, or why would some of them work?)
...
Because when calibre sends an AZW3, by default the embedded cover is updated.
If the book is a PDOC, the *Kindle* extracts the cover.
If the book is an EBOK, calibre additionally sideloads the cover thumbnail.
Any way you slice it, I don't know why the Kindle would use the old cover -- or even how it could get the old cover.