Ok, from both my personal experience while in service and a little light collecting. In 1987 I was issued what was essentially a LNIB M16A2 when I arrived at my first duty station. I don't remember the entire serial, but all the M16A2s I carried over the next 4 years and 2 duty stations (USMC) were in the 61 or 62 mil range. All the furniture was similar in texture as what you find on A1 furniture, smooth and what could most correctly be called semi gloss. Not shiny, not flat just a faint buffed look to it. The PG had a slight grippy texture and got a little shiny after usage. The heat shield did not have "do not remove" (hereafter "DNR") on the inside. I got out in 1991 and stayed out until 1996 when I join the NG. Oddly enough the unit I joined had M16A2s and they were used. I do not recollect any being restamped M16A1s but I didn't really pay attention to any but my own, and it was a Colt and the furniture was similar to what I used my 4 years in the Marines, except now the hand guard heat shields had "DNR" stamped in them. We all removed them for cleaning anyway. In 2001 I got issued a LNIB FN and the stock was the same as before, not the ashen gray looking stock, and the PG was more glossy than usual and the HGs were dead flat with "DNR".
Now on to what I've collected.
I have what seems to be unissued early A2 HGs, complete with the early shields. The area exposed under the HG holes is a strip dyed greenish gray.
I have a single shiny HG and the shield is stamped "DNR" in skinny text and there is no dyed strip where exposed.
I have a single HG that has a sand blasted texture that is smooth on the raised ribs. The shield has a fat text "DNR" and the dyed strip looks sprayed and almost has a 2 toned appearance.
I have a set of what I call FN HGs, they are take offs and dead flat, fat text "DNR" and sprayed dark gray strip.
I have a set of late A2 HGs, dead flat, skinny text "DNR", almost black dyed strip and the shields are glued in.
I have decided not to get into the commercial HG sets I own.