The FAT partition header has always had an ID field, the OS could request you to reinsert a removed disk and would know if the wrong one was inserted. Also, on

The FAT partition header has always had an ID field, the OS could request you to reinsert a removed disk and would know if the wrong one was inserted. Also, on single-floppy systems there was a virtual B: so you could do disk to disk copies just by saying "copy A:foo B:" etc.