I have more craftsman ones like these for sure, just never noticed the date code stamps.
Hey, Z, I don't have any postwar ratcheting DBE wrenches. That is to say, I don't have any that are new enough to be Lang patents to check for you, and I don't have any Snap-on tools from that era, either, so I am not as familiar with the date codes.
Are you sure those are Snap-on date codes? And have you checked to make sure they logically jibe with the award dates of the patent numbers shown?
If the answer to both of those questions is yes, ...
/ One conclusion might be that Snap-on was making them for Lang's company (A&E Mfg Co, in Racine, WI), truly 3rd party, as it were. In other words, Mac and Craftsman (and ostensibly many others) acquired them from Lang, but Lang was outsourcing some production to Snap-on.
/ Another conclusion might be that Lang was making them for Snap-on and simply used the same production process, including the date stamps, for other brands, intentionally (for their own customer contractual, warranty purposes) or unintentionally (routine).
I'd have to say I favor the second. Which is kind of cute, if you think about it. Snap-on has no actual trademark on the codes.