The 1, 2, 4 format codes are universal across all labels. I'm not sure when they were introduced, but it's possible it coincided with the emergence of CDs (or perhaps when the barcode system began to be used, which is more or less around about the same time?)

Minidiscs were given the number 8, so not only are we now looking for 3, but also 5, 6 and 7 (at least)!