The soft matte insert is just too hard for your feeble brain to comprehend.
As soon as you apply another element you need to reprocess the image and an inescapable result is that it introduces a new layer of film grain, which is instantly detectable.
Also we have two angles of Kennedy's head so even if you can avoid the excessive grain structure then you have to have a "stand-in" which needs to be photographed under the same lighting, with the same perspective and from an exact identical distance because even a minute change will mean the film grain will be out of scale and again instantly detectable, it's not as easy as you Noobs think.
At the end of the day the Autopsy Photos were NEVER meant to be in the public domain and the only reason we have them is because a CT leaked them. So to think that they altered the private medical photos of Kennedy's autopsy just in case they were leaked is absurd and really over thinking the problem.
What was photographed was Kennedy and the injuries in the photos are what happened.
Btw what is a "soft" matte insert? And then point out exactly where your "soft" matte insert exists in the following image created from a stereoscopic pair of autopsy photos and tell us how they created this mathematically accurate marvel?
JohnM