Smae here - and for the last 15 years on the Tandy CoCo3. I have used for years, the Mitsubishi M4853 DS/QD drives on the CoCo, and DS/DD media.
DS/DD and DS/QD media is basically the same. AS others have mentioned, they might have done testing at 96tpi DS/QD to certify it, but the media and coating is the same.
Only difference, is that the the DS/DD is 48 tracks-per-inch using 40 tracks, and DS/QD is 96 tracks-per-inch using 80 tracks. Basically, the DS/QD drive put 80 tracks, or cylinders, in the same space that a DS/DD 48tpi drive puts 40. Density is the same: 512 bytes-per sector, 9 sectors per track IBM standard (others may differ a little, obviously) but it is still double-density. a high-density 5.25" is 15 sectors-per-track, and uses different media on the actual disk, and a high-density 3.5" 1.44MB disk is 18 sectors-per-track, and again, uses different magnetic coating than what is on a 3.5" DS/DD 720KB diskette.
Long story short: DS/DD and DS/QD 5.25" media are virtually the same, and I have DS/DD disks that have been in use as DS/QD for over 15 years, and are still readable.
T