In this fine and valuable post, terms used are a bit fluid among interviewees and the author. The author makes distinction between use of an optical effect (an inserted traveling matte, not used) and aerial imaging (painting in the forward head wound, skull "flap," and skull explosion). Rutan, however, cites the forward wound as an "optical" effect.
The forward skull "flap" is rather realistic looking in Zapruder. Is it possible that the forward wound is actually a filmed image of the rear wound transposed to the right front, through whatever means? Combination of traveling matte for the "flap" with aerial imaging used to create the skull explosion?
Appearance of a manufactured right front "flap" in the autopsy photos would require taking the time to review the doctored Z-film and replicate the altered frames.
Alternately, what's up with all the black over the parietal area in the "stare of death" photo? Check full size at link https://en.wikipedia.org/wiki/Autopsy_of_John_F._Kennedy
The frontal wound images and records need some further examination.
Good one, Keven.