GC--
Thanks for your question, and it is a fascinating one.
Connally: I was knocked over, just doubled over by the force of the bullet. It went in my back and came out my chest about 2 inches below and the left of my right nipple. The force of the bullet drove my body over almost double and when I looked, immediately I could see I was just drenched with blood. (1 HSCA 42)
In my layman's review of the Z-film, Gov. JBC is pushed forward ~Z-295. That's my best guess of when JBC is shot.
There is an additional curiosity that the slug that slammed JBC's wrist entered through the dorsal side, or about where you would normally wear a wristwatch face. That is what Dr. Gregory said.
The problem is, that is nearly anatomically impossible, if the bullet first passed through JBC chest. Try touching the face of a wristwatch to your chest.
I don't know when JBC received his wrist wound, or from where it came.
My contention is JBC was struck from behind ~Z-295.

My contention is JBC was struck from behind ~Z-295.At Z295 JBC is lying back in Nellie's lap.
Perhaps I'm missing something but would it be possible for you to explain, in a sensible way, how he could be shot in the back from the Sniper's Nest in the southeast corner of the 6th floor of the TSBD building while lying in Nellie's lap.
Or is it your contention that Nellie shot him? I don't really follow what you post so I'm not sure.
As for JBC's wrist injury...note that after he begins thrashing about in the limo (starting around z225), when his wrist emerges from behind the limo door it is bent at a really unnatural looking 90 degrees.
Also note that in z222 we can see the white of his shirt cuff just above the door but this disappears in z223 (because his wrist has been hit by a bullet). He then commences to thrashing around.