Oh magnetic disk formats can get wild. :) Before everyone settled on the MS-DOS format, there were so many variations, and lots of tricks to get extra capacity, speed, compatibility etc, etc. Mixed density disks were easily a thing and that's quite possibly what your DD CP/M disk is if you can read the directory but nothing else. The directory would be in track 3 or 4, BTW, near the outside edge.

We have a dozen OZ-1's in our wharehouse