MAC DBE - Markings & Meanings

The model numbers on these wrenches is consistent with the 1949 catalog (B-###), but changes to the newer style markings in the 1951 catalog.  The purpose of this investigation is to determine the meaning of the "0" stamp after the model number on the shanks of these wrenches.  The first two pictures show wrenches in our collection, while the third image comes from member Chopper.  At first we thought it might be an owner's mark but with Chopper's examples added to the fray, it proves this was a factory marking with a meaning.  Perhaps an early idea of stamping date codes?  The "0" representing 1950 would make sense given the model annotation changeover timing.  We'd welcome thoughts on the subject.

Image Description: 

Double Box End, deep offset wrenches.

Image 2 Description: 

Markings from above wrenches:

Image 2: 
Image 3 Description: 

Member Chopper's examples:

Image 3: