Isn't it also a bit odd that they would mould a stunt in order to produce a hero? However, the MR piece also bears more resemblance to the stunt than it does the hero. To me, the stunt and the hero look like two completely different helmets, especially in the grin.
Just like they said, the hero and stunt helmets came from the same mold. It was assembly and painting that made them different. If you make a new mold of one, you have a mold for the other.