Actually, 100 TPI drives were not that common IIRC but three or four manufacturers did make them; aside from the stepper mechanism they were identical to 96 TPI drives.
The diskettes themsleves were all the same physical material and of course blank diskettes don't have tracks per se, so it's always been a question of quality and certification. I think in the old days when manufacturing techniques and quality control were relatively primitive and diskette prices were high it made sense to actually test disks and certify them for the narrow heads of 96 or 100 track drives, leaving the 'rejects' for the more forgiving 48 track drives with wider heads. As time went on and overall quality control improved, pretty well any name brand diskette that left the factory would be good enough for the higher density drives and most people believe that it became largely a marketing issue, charging a higher price for QD labelled diskettes until the PC made them obsolete.
Like I said, IMO the important thing is to not mix formats on the same disk, e.g. use a diskette formatted for a PC in a CBM (or Apple, Atari, etc.) drive, without first bulk erasing the diskette to remove the incompatible format.
And of course the HD (1.2MB) diskettes used in later PCs are a different kettle of fish, a different material and not at all compatible with the DD or QD drives that almost everybody else had been using.
Of course none of this helps Alex; let's hope that cleaning the heads and rails and using a nice freshly erased diskette does...
your suggestions great!