These Serial numbers are in all CGE games, I guess White Goblin just use the same printer and specs, so the Serial number is in that game as well.
Occasionally CGE asks for this number when asked to provide replacement parts, the most common time I've seen this is when there have been misprints from first printings of Essen releases.
I think it mainly helps identify where it was in a print run, so if a cluster of errors are spotted in Serial codes they can address the issues with the printers.
Oh this makes sense, I didn't notice it in my codenames(words) box who came straight from essen, but it was under the insert.
Thanks for the info.