Here's merely an observation. The earlier A's and B's engraving was not as extensive as later guns. It appears (to me) that the later guns were more finely engraved, (less "cartoonish" as far as the dogs) but my opinion is only due to viewing the one's I've seen come up for auction. I've passed on a couple due to this reasoning.

Regards
Ken

I prefer wood to plastic, leather to nylon, waxed cotton to Gore-Tex, and split bamboo to graphite.