I know that back in the day when 5.25" floppies moved from 360 KB to 1.2 MB, there were lots of problems with low-density disks in high-density drives, but I have never had such issues with 3.5" disks. (During the transition from 360 KB to 1.2 MB, it was fairly common to see computers with one of each type of drive, for better compatibility. My old IBM AT is that way.)

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In the early days (1984/85/86) there was a huge difference between Single Sided and Dual Sided single density 3.5" disks. I had a lot of 400K disks that would not format at 800 k when I got my 800k drive. Then the 2 MB 3.5" disks DSDD (1.4MB formatted) were introduced and you had problems again with 800 & 400k drives using them. By 1988 things settled down and you could use 1.4MB MS-DOS disks and reformat them to 800 k ok. I must have recycled a 100 of those free AOL disks that eveyone was getting. I'd get a bunch of them and have a formatting session and I used a hair dryer to peel the labels off. [8D]

In 1984 I went into a computer shop and paid $5 a SINGLE blank TDK 3.5 inch disk. 8-o They were $25 for a box of five. You could also buy 3 inch disks but that's another story!