I wrote:
Now I'll try to go back through my logs and try to see when sdubby got installed and why.
Jonathan Billings wrote:
Once you've verified it boots into new kernels, feel free to delete the /boot/efi/$MACHINE_ID and /boot/efi/entries directory, so you aren't wasting space on the EFI volume or preventing any future attempts at booting from those files.
I can't tell when sdubby got installed. My logs go back about six months but the only references to sdubby are "upgraded".
I also found that, even reinstalling kernels did not completely fix the contents of /boot until after I had deleted /boot/efi entirely. (Well, actually, just moved it elsewhere. To be deleted eventually.)