Entry wound in JKF's throat proves more than one shooter. JFK getting hit with a frangible round in the head proves there was more than one shooter. If the bullet that hit JFK in the throat came through the windshield, that proves more than one shooter.
Summing it up, both JFK and JC were hit by bullet(s) coming from the rear of them. JFK's throat wound came from the front and the frangible round that hit JFK in the head came from the rear.