Thanks Michael. I tried renaming Hierarch.pm as you suggested, I saw no other "Copies to self". I don't remember doing anything special Jan 13th, but I might have moved some messages to similarly named folders in an archive subdirectory. But I've been doing this sort of thing successfully for years.
I do have plenty of backups, I can go back to the state as of Jan 13th and compare. If I revert I'm not sure how to rescue the more recent messages.
One thing I just noticed. In my old version, the Copy to self folder was kept in a file called copyself.pmm. It's not called this in the current version, but in trying to debug this I deleted and tried to recreate copies to self.
(later) I tried this. I composed a new message and looked to see what files had an updated time stamp. There is a file called FOL068E0.pmm that was updated and seems to have some recent sent messages in it. But this is NOT the file associated with the "Copies to self", which is FOL066A2.PMM. I feel like I am making some progress. I don't care if I lose two weeks worth of sent messages, I just want to get back to being able see messages I sent.
(still later) I found a workaround. I made a Copy self rule that matches every message and copies them to my "Copies to self". My"Copies to self" folder is now populated, but I don't think I fixed the underlying problem The sent messages are still also going to the invisible folder FOL068E0.pmm. Any hints about how to make that folder visible would be appreciated.