Thanks for the compliment - not many folks find "beauty" in the H&Rs, much to my continuous dismay.
As to grip differences - the mono-grip was totally "portable" - one will fit (almost) any other gun - so they are often switched or H&R made use of what ever they had on hand until older stock was gone. Thus, you can find wooden grip on guns made in the mid '40s that should have plastic grip - or as with the one I pictured with the "stag" grip, have a 1950s grip on a 1940s gun.
The "strange" cuts were a carry over from the black powder and semi-smokeless powder days - the "relief" cuts were made to help blow firing residue and gunk away from the forcing cone-cylinder interface, where a heavy build up could inhibit the cylinder from revolving. H&R got away from making those extra cost cuts at some point during the war years. If you look at that area on the Manual Ejecting Model 925 (mis marked as a M25 on the pic) you'll see that the relief cuts are missing and the forcing cone is now flat faced. You can do that with low residue, smokeless powder that doesn't foul the areas around the flash gap.
Still don't have any idea about the '16' stamp - never saw one marked in that way. Any chance of pics?????? I'd really appreciate seeing your DEFENDER 38.
I included the pic of the case color hardened extractor simply because I've not seen one in that condition on any of hundreds of H&R revolvers that I've owned or examinied. I image the case coloring would be worn off or reduced by usage - that gun being NIB - allowed the rather thin top layer to remain behind.
BTW, my first name is JIM not Mr.