Sounds essentially like a dead-end given that the listings go back - what? A year or so? Coincidentally I see another 21.2 variant, this one with a single pellet above, and a single pellet below the crescent, just listed today. Without records going back beyond 90 days, at best a snapshot of a small sampling could be made. If all records had
been available, a more substantive picture might have emerged, perhaps even with some die linkages determined.
Alas, I wish I had
more time for the research this would entail - even for the snapshot version. I just have too much on my plate. Retirement can't come soon enough...