I’d have still expected them be writable because unlike CDs, writing a magnetic field isn’t destructive. But what I meant was whether cheap blank disks used a slightly different (cheaper) magnetic alloy with a shorter read/write limit than commercial software where they maybe spent a little more knowing it needed to be read often?

I do remember cassettes had different quality magnetic strips but I don’t know if the same was ever true for disks too… so it’s probably bonkers. I’m just throwing some ideas around without much thought. :)

It might just be a case that college kid me was less careful with his disks than you were.

More recently though, I have unboxed my old collection of 3” (not 3.5” but literally 3 inch) floppies for the Amstrad CPC 464 and they almost all worked despite being nearly 40 years old. So I definitely believe you when you post about your success rate.

It depended on which brands of floppies you bought. Some vendors were more profit-oriented than others and would skimp on the binding agent or just the amount of magnetic material without which the signal can become so weak they could become corrupted by being the the same room as a Wooly Willy.

That was one of the earliest instances I remember, where superior functionality was shipped with a product but kind of locked up. And like some other such “locks” they were easily defeated.