S/42 Magazine with no serial number

[Nazrat]

Is a magazine that has S/42 stamped on the bottom, but no serial number something that would have been produced, for the purpose of replacing a lost magazine in the field?

The gun that it 'came in' is a 1916 Erfurt (now with a 6" Bohler Stahl barrel), so I realize that it wasn't issued with the gun.

Thanks,
Tad