FDS disk code stamp located above label

[Phosphora]

I was curious if there was any significance to this stamp (Serial number?) that appears above the right side of the disk labels on the all of the disk's cases? Is it just a random production code, or does it have some meaning?
(Is there a series of codes only used for one particular game, are there codes that were only used for blank writer disks? Date of manufacture? Etc,etc)