[MisterTea]

This reminds me of a less interesting story:

My father bought a 386 for his work to replace a 286 which only had a 5.25 floppy drive. The 386 had both a 3.5 and 5.25 floppy drive so he quickly switched to the more sturdy 3.5 disks and moved a lot of work to the 3.5's.

Everything was working great until he got a second similarly spec'd 386. For some reason the machines couldn't read each others 3.5" disks. So he called his programmer friend who stopped by and did some testing. Both machines could format/read/write their respective disks no problem. So he formats and writes a test file to a disk from each machine and takes them home with him.

My father gets a call from him the next day: "call the vendor and have them give you a new 3.5 drive in the original machine" Turns out the heads in the original machines 3.5 drive were slightly misaligned mechanically to the tracks. This caused the disk to be perfectly workable in the bad drive but fail to read in any other machine.

[RuggedPineapple]

Somewhat related, but as 800k floppies got harder and harder to find, it became common to just cover one hole on a 1.44 mb floppy so the computers that used them (mostly old compact macs) would treat them as 800k disks. This is fine in the short term but since the tracks and what not don't line up quite right it'll usually degrade over time.

[Zardoz84]

This remembered me when I had a ZX Spectrum +3 as child. At some point, a belt broken and my father replaced with a different belt. So, it can't read anymore my old floppies. I can only use the floppies if I formatted again.