Tom, in your process where some albums had cover art for one or two songs. You can, "get album info" and if the artwork shows up in the artwork tab there you can drag it slightly and re-drop it to copy that art to all of the songs. That seems to work if the first song on the album has the art, if it is a later song you need to, "get song info" and copy that art, then go back to "get album info" and paste the art for all of the songs.
Either way this has been an absolute disaster of a transition for Apple's faithful iTunes customers who aren't bought into the subscription based Music model. We will continue to be thought of last going forward as we are not a constant revenue stream. I hope Apple considers the impact of how releasing us from that tie into the overall Apple ecosystem could affect the customer base for all other things apple going forward. Although we will continue to be a smaller and smaller group of die hard fans.
I know I was hooked into the apple ecosystem with the first iPod, and that connection via iTunes consequently led to purchases of around 10 mac computers, full home airport networking in numerous homes, dozens of @TVs, iPhones and iPads from the first models of each onward.
Given the shift of focus to all subscription based value, and the erosion of the, "it just works" tenant I will slowly become less bought in.
Hopefully someone sees these threads and provides some transparency surrounding future fixes, and when we can successfully transition from Mojave and iTunes to Catalina and Music without the massive technical debt created by the cover art debacle, and memory leaks...
Otherwise we are left guessing.