Actually there were 3 types of the front tip - the originals had no pin - the 3 blades came together to form the tip. Later went to a pin in the tip - that is the 3 blades had a slot to receive a cylindrical pin that added strength to the head. The third was the replacement of the pin with a cone with a pin sticking out the bottom. The pin from the bottom went into the same slot and the cone, when ground, became the pointed tip. If you look close you can see the brazing and determine pin vs cone/pin. The old ones had the square cutouts in the back of the blade, as noted above. Our older heads (say mid-80's and before) were spray painted by hand with rustoleum. From the mid-80's to the time Delta bought the heads we dipped them in rustoleum - the spray paint probably leads to the "textured" finish someone mentioned.
We never sharpened the back of the blades commercially - if heads were bought that way it was probably something someone asked for and was done as a one-off. We always have sharpened the trailing edges of our own heads, but never sold them that way on a large scale.
Occasionally I see some colored ones - that would be primer red, primer gray, or primer tan. Just shot with the color over black. These are 2nds that did not make the cut as "firsts" for some reason - usually the grind is uneven blade to blade or a bit of brazing is missing somewhere. These we sold out of the house for $1 each for years. No problem using the heads, that is all we ever used ourselves, but not anything "special". Magnus did some with white spray paint too.
There were some late Rothhaar heads that were Teflon dipped. This would have been 1989-1990. There were some green coated and some black. These are probably some of the first Teflon dipped heads made. Dad tried this out early on as a possible improvement to aid penetration. I killed the first big game animal with one in 1990 - a 6 pt in Ohio. Didn't make any difference that we could ever tell as far as penetration goes (shot through pretty much everything either way) - it seems it is still a good marketing gimmick for some heads, though.
Biscuit cutters, now THOSE are hard to come by!
Ryan