I can't remember seeing any original 1967 units that didn't use the round tag.
Early 1968 Pontiac carbs were also round tag, then at some point they will be stamped, and dated on the baseplate.
All Service Replacement carburetors were stamped, aside from a few with no numbers anyplace. In almost all cases the SR's are missing the Plant Code and dated later than the model year run.
I hate to say with any of this stuff that ALL of them are that way, as we keep seeing exceptions to the basic rules.
Just last year I saw my first Ram Air manual transmission Service Replacement carburetor. It was a 7040273, had the correct Plant Code, but dated also two years after the production run. It breaks all the rules with these things, and it was the real deal, never been molested in any way.......Cliff