The first time I cleaned out the old IIIc I had, about a dozen or so tiny bits of film, the broken sprockets cam out of what was a very 'clean', working camera, which were impossible to see with just a torch and eye.
I have long since come to believe that such bits naturally accumulate with normal, skilled use, as that camera had had a CLA and new curtain done/installed by the seller just a few years before it came to me.
Old FSU FED cameras and other Barnack cameras all seam to share this vulnerability.
IMO..