Maybe bulletproof is a bit strong but I mean, it was fine on DOS/Windows for decades. I never lost data due to filesystem corruption on those computers. Media failures, yes frequently in the days of floppy disks.

Running scandisk and chkdsk was also a thing for decades. Luckily the lost sectors were often in unimportant files. But definitely a gamble.

The bulk of the safety came from the redundancy of copying the file across machines, not filesystem protections.

I had a HD fail on me while using Windows 98 as main OS, yet thanks to ext, I think it was ext2 at the time this happened, I still managed to repurpose it for Linux, for several months.

It was ok from possible data failures point of view, I didn't had much data other than the distro and the stuff I also needed to compile under Linux.

Somehow it managed to still work with the disk, with the sectors that were not damaged.