. . and you can still get this sort of problem. The worst nightmare is a power failure just long enough to damage the OS but not long enough to kill it. I've seen that happen a couple of times over the years.
I have carefully examined a couple of cases like yours and found what had happened was a block of data was written to a disk address occupied by the FAT table. Why was it written there? As I've told the clients, "Nobody will ever know".