3.5" floppies were still common while I was in college. I have distinct memories of copying a project to a floppy in my dorm room, popping the disk out, walking next door (literally next door in the dorms, not even going outside up or down stairs or anything), popping the disk into a team member's PC and the project being gone. We laughed it off and chucked the disk in the trash and got another. Project wasn't lost-lost since I had a copy on my hard disk. This was also the era of the 100MB Zip Drives, which I also had in my PC and thankfully all of our lab PCs had, too. That's what I normally used for all of my day-to-day file transfers of any real import. I still have my zip disks, but I seem to have lost my zip drive, so no idea if the disks still have any data on them.

I was on a school paper in high school and was taking photos on a "digital" camera that wrote to 3.5" floppies. Some of them are still with the (printed) copies of my articles I kept. I'll have to see if they survived.

This is probably my "I'm getting old" moment. Good lord.

We used to copy files three times, better onto three separate floppies

Yeah at the time. You would get the whole range of good/bad disks. Sometimes even between computers. May work just fine on one computer and not the next. It was not common but it wasnt totally rare either. Just sometimes would catch out out at silly times.

That they are still used in a critical infra item is a bit surprising. Getting new stock would be a major hassle.

I said this in a parallel thread but 3.5" disks were much less reliable for me even in the 80s with the Amiga.