Hi guys.
Some news. I discovered some pictures of original prop of the Denver Art Museum Exhibition(and thanks to Dan H. and Jay D. for their photos!!) that confirmed what I thought.
We know that news suits were made for ESB and then re-used for the other episodes (according to Don Bies. Informations reported by Jez of StarWarsHelmets.com).
So the ANH C 3PO is a little bit different (I only focus on the helmet).
To me, the ANH helmet is narrower (and could explain why it was umcomfortable and improved for ESB....thus wider....only speculation, I don't have official measurements).
The way the faceplate fit to the back is different. Were the ESB style have this offset to fix it (you certainly all have this on your replica)
, the ANH faceplate is totally smooth and slide inside the back. Plus the bottom of the faceplate doesn't fit well and you can see and screen grab, a space between each elements.
Finally, the ANH can be identified due to his very sharp line on the right side, from the eyes to the end of the faceplate (more limited on ESB faceplate). Plus the top is a little bit curved. And thus the back have a kind of notche on the horseshoe to allow face to slide inside
I'm really sorry about my poor explanations due my poor english (lack of vocabulary). So I made this medley pictures (and yes there is a K 3PO because I assume it's an ANH helmet repainted).
Click on the link for a full sized picture:
https://imgur.com/fB9OzAz