When one accepts the reality of the Single Bullet Theorem, i.e., that JFK and JBC were struck by CE-399 at approximately Z-222, then one can speculate on whether or not it was Oswald who had fired the earlier, missing-everything, shot, and if so, when he fired it.
Since three spent shells that had been fired from Oswald's Carcano were found in the Sniper's Nest about an hour after the assassination, since the Carcano, with Oswald's prints on it, was found on the sixth floor, and since Oswald was seen on the sixth floor near the Sniper's Nest by Charles Givens at about 12:05 and by Roy Truly and Officer Baker in the second floor lunchroom about 90 seconds after the final shot, we can reasonably assume that that it was Oswald who had fired all three shots.
Now the only remaining question is when he fired the missing-everything shot.
Brian Roselle and Kevin Scearce point out in their 2020 study that an involuntary "startle" reaction to a loud, unexpected sound like a gunshot does not involve a major L-R head rotation, but "flexion" movements (bending the head and neck forward and downward), instead.
They also point out that seven prime witnesses (including five passengers in the limo: JFK, Jackie, JBC, Nellie, and Kellerman) quickly
turned their heads within half-a-second of each other between Z-142 and Z-149, indicating that Oswald's missing-everything shot was at hypothetical Z-124, half-a-second before Zapruder resumed filming at Z-133 and 2.02 seconds before Croft took his photo at Z-161.
Rhetorical question: Can even three of those passengers be shown to have
turned their heads quickly within half-a-second of each other in any other part of the Zapruder film up to Z-222?
I haven't looked yet, but I rather doubt it.
https://d7922adf-f499-4a26-96d4-8ab2d521fa35.usrfiles.com/ugd/d7922a_e280e26982b44f2c97c6e6e27026e385.pdf