JBC has always been clear that he was hit and said "No no no" after he was turning back towards the front well after frame 223. Nellie said he was hit right AFTER saying "No no no". Here she is at 5:19.
Nellie always maintained that JFK already had his hands to his throat when JBC did his turn around and before JBC was hit.
JBC said even after turning around he could not see JFK out of the corner of his eye. With JFK behind and slightly right tf JBC he should easily see him when his head turned only 90 degrees. The reason he couldn't see JFK could be because JFK was already leaning to his left.
JBC said he fell almost immediately back onto Nellie once shot but if he was hit at 223 he did a full turn around to look for JFK before falling back on Nellie.
I think the clearest version of the events should come from Nellie as she was an observer that was never hit. Her description of seeing JFK raise his hands well before her husband was shot is very credible and matches JBC's version.
If Nellie was still looking towards the President at the moment of the second shot, and she thought Kennedy's hand-lowering (beginning in the Z190s) was the beginning of a reaction chain that led to his hands being at his chin, then she might assume he was struck on the first.
Mr. DEVINE. Then what is the next sound you heard? You were
still looking back at the President. Did you hear another sound?
Mrs. CONNALLY. I heard the second shot; yes.
Mr. DEVINE. The second shot. Were you looking back at that
time or were you looking forward again?
Mrs. CONNALLY. I don't know.
Kennedy works his hands towards his throat in about five frames, or 1/3 of a second from a hypothetical shot at Z223. Easy for that to morph into his sweeping hand-lowering. Kennedy may have also stopped smiling if he saw the Umbrella Man protester on the sidewalk as the car approached the Stemmons sign. If that happened, and Nellie noticed it, it could have influenced her belief he was hit by the first shot.