I am not sure what your question is Apparently when someone describes serious discrepancies in the film they saw originally and the one we see now the implication is film has not been altered?
It only really implies that the image Dino was being shown didn't quite look the way he remembered it did when he last set eyes on it 50 years before. Could that mean it was altered? Possibly, but you need something stronger that "hey, I don't remember it this way." Especially when one of those "I don't remember that" things resulted from Janney telling Brugioni something that simply isn't true.
Now for a kind of thought experiment:
When you think of frame 313, what image comes up in your minds eye?
I'll bet your brain is now full of the terrible picture of John Kennedy's head enveloped in a horrific halo of bloody mist. Maybe the image includes Mrs Kennedy's puzzled face obscured by said halo. And maybe some of the limo. Extra credit if you saw Greer still looking around behind him.
I'll bet you aren't thinking that the top 80% of the frame is an image of the grassy lawn between Elm and Main, or that Toni Foster and her coat appears mid-stride left of center, walking across it. Some people well-versed in the film remember seeing Clint Hill about to catch up to the bumper, but he doesn't appear until about frame 330.
I'll also bet Brugioni is just as liable to the same self-selection process that blots out Toni and the lawn to concentrate on the limousine proper, and the awful deed being played out there.
For that matter, they made enlargements of the Zap film for the briefing boards. I'd suspect that they cropped out a lot of the image to concentrate on JFK and the limousine. That image of 313 would definitely put the "scatter" well up in the resulting image.