Hello,
A good question! I am fairly certain that the version WITHOUT the bizarre inclusion of the pilot's head is the (in my opinion superior) original. I think the original US version was issued without the pilot's head; then, for some strange reason, the pilot's head was added for the release by Revell UK. If I recall, this is how Brad Hansen described the sequence in his book "WWI in Plastic."
The original is one of my all-time favorite WWI aviation paintings, no doubt influenced by nostalgia as it was one of the very first WWI kits I built. The composition, the details of the delicate yet menacing Eindecker, the tracer bullets standing out against the smoke trail of the opponent, it's all great. If you needed one image to exemplify the "Fokker Scourge" of 1915-16, this is it.
Then, when the kit was issued in Britain, they inexplicably decided to add the strange pilot's head in the lower corner, and added the "bronze nameplate" which sometimes appeared on Revell kits. It spoils the whole composition. I don't know if Knight had to paint over his original, or how it was achieved.