They had 2-for-1 at my local drug store for 91%, so I grabbed that.
I'm going to clean my dead floppy drives anyway to make sure they don't damage good disks, and then use one of them for "screech testing" on unknown floppies. If it doesn't screech on the bad drive, then I can safely move the floppy to my good drive and attempt to read it.
I mentioned in a PM that I'm going to take some autopsy pictures of the disks. The disk is a dull brown and not the shiny black as compared to another floppy disk. I don't know if this is just a difference in manufacturing, or if it's discoloration from some sort of degradation. If it's degradation, then it could be an easy-to-see visual clue if a disk might hurt your floppy drive.