That is funny of course (in hindsight), at least if you tried to save on 1.44MB 3.5" floppies. When I was restoring all of my old tapes and floppies I could recover nearly all my 9-track CCT tapes, nearly 100% of my 5.25" floppies (various densities, including 1.2MB), many 720KB 3.5" floppies (8" ones are also good) and zero 1.44MB 3.5" floppies. Discussed this with many other people who had basically the same experience with HD 3.5". All of these were stored in the same physical environment. Some other tape media weren't particularly good (exabyte, 4mm tape etc, but then again those used to fail at the very beginning).

Interesting… all of my dad's 5.25 failed.

If all the disks failed it could be the recording drive, assuming they weren't separately verified at the time or writing or since.

Our school's collection of BBCs included one drive that could read everything, including data it had created, but most of the other drives would reject anything it had written. Once identified that drive was taken out of general circulation and only used to read data for writing to a new disk in a second drive, and eventually skipped once it was unlikely any data someone cared about had been written by it and not copied elsewhere.

This often comes down to regularly testing old data. Floppies shouldn't have been used for archive storage but often were, with a problem only being noticed years down the line when the data needed to be read. Other media similarly: recorded CDs and DVDs from a decade or more ago are sometimes not readable now. An archive is only an archive if you can actually read it, much like an untested backup is just a hope not really a backup.

X68000 designers had some foresight. Compact version, not so much.

Is there any way to recover the failed disks? Or are the bits lost forever?

There are tools that record the actual magnetic flux from the disc, over multiple passes. In skilled hands, this has resulted in some "irreparable" discs being recovered. The most prominent one I know is KryoFlux.

Might be because 3.5 disks outnumbered in production quantities any other kind of floppy disk, thus the average quality was lower? Massive production lowers costs, so to keep sane margins they just decreased quality? Or is there any theory about the technology itself being less reliable?

From what I've gathered the issue was simply that for the HD 3.5" floppies the density was actually more than the medium could take. 720KB had lower density and didn't have that problem.

A friend in high-school used to do the old trick of copying a DLL onto a floppy disk, renaming it "essay.doc", and handing it in to the teacher. Next week he'd feign concern that the disk must have got corrupted somehow, but by then he'd bought himself an extra week to write the paper.

It was a different time...

I had a QuickBASIC program that'd spit out a generic disk error screen, and later a Visual BASIC program that'd put up a Windows dialog saying that it needed to be open on NT 4 or later (school system was Win9x at the time). Good to hear we all slacked off the same :P

A friend of mine in college (much more recently) did a similar trick with Google Docs - "oops, forgot to share it with your email."

Students adapt to the times...