Today, I took a not-entirely-on-purpose break from ripping to puzzle out what the duplication problem was. *shudder* I still don't know, but I've deleted all the duplicates. I think. I also deleted some other stuff, but fortunately, Match had already run, so it just gets replaced by itself with a little you-can-download-it icon.
Wow that was taking up a lot of storage. Wish I knew why that happened. I'm monitoring each upload now fairly closely to see if I can spot duplication when it occurs.
I then went to figure out why this had happened on my iPhone. I also failed there, but did learn how to delete them (left swipe). It's unpredictable which of each pair is the one stored in the cloud. _Really_ unpredictable. So I wound up having to guess and frequently deleting both of a pair to get the not-in-the-cloud one.
Hopefully this will never, ever, ever happen again, and will remain a mystery of the years when Apple was transitioning from you-do-everything-on-your-own-computer-w