My guess is that there may have been a very few reported problems with the G dates, Thor. In an attempt to simplify the machining process for greater mass production, they may have created an error, that was subsequently remedied after the G dates.
Perhaps documentation was lost on this, but it seems unlikely that a "solution" would have been re-instituted for a non existing problem.
Since this was the era of the "sneak" Lugers, maybe the reported problems factory paperwork may have been lost, misplaced, or destroyed.
The old saying "don't fix it if it ain't broke" springs to mind.
Just a hypothesis, of course, but that would be my guess.