Numbers on C-4 spark plugs

[1crosscut]

I've started working on cleaning up some C-4 spark plugs. After taking several of them apart I've noticed that there are numbers towards the bases of the porcelain that are hidden when they are assembled. Most have a number but some do not.
Any idea as to what the numbers represent?

 

[J Franklin]

Pre bar code

 

[katy]

I would guess some sort of production code.

 

[1crosscut]

A mystery that may never be solved.

 

[Sunnybrook Farm]

Probably which machine made the part, if there was a problem they would want to know where it was coming from.

 

[katy]

Have you tried contacting Champion?