This is my experience in helping date the heaters as you have them detailed with some clarifications.
1. This is a carry over heater used in cars trucks back to at least 1941 and perhaps earlier. It is common on Chevrolet and GMC trucks 1947-48 as stock was consumed. This heater appears in my 1947 and 1948 (just has drop in updates) Salesman data books. the GMC/Chevrolet versions carry a unique identifier plate on the front for each make.
2. There are at least two versions of this heater in trucks (a modified version was available in cars with a shroud as shown).
https://www.flickr.com/photos/advance-design_parts_co/8129344483/in/set-72157631868452754early version 1947-some 50's comes with an aluminum plaque and has corresponding slots for it to fit into. My 1950 3600 (original owner) was equipped with a plaque recirculating heater. I have owned six other 50's and it was a mix of the two.
https://www.flickr.com/photos/advance-design_parts_co/8129304429/in/set-72157631868452754The later version comes with a decal (no holes)some 50's through 55 1st (color changes apply for certain years and GMC/Chevrolet).
https://www.flickr.com/photos/advance-design_parts_co/8129330842/in/set-721576318684527543. As described except the early versions as described above are punched for a plaque, sometime in 1950 this changed to a decal? All of the 47-55 1st heaters were accessories except the 1947 version of the Air Flow which in the 47-48 Salesman Data Books has an R.P.O. option number (I am traveling so do not have ready access to list it).
4. As described, there are color differences and these heaters all have decals.
As I stated earlier I have never seen the "oddball" mentioned in the previous posts but would love to if someone has one.
