I can accept your endpoints for a spent #2 and #3, but not #4.
You write-: "When does #4 stop Accelerating? #4 decelerates when the Left Arm stops accelerating away from your chest which is "Both Arms Straight" or further hopefully, if possible."
You "seemingly" believe that the left arm is accelerating to the end of the followthrough. I cannot understand that point. In a pivot-driven swing, the inert left arm gets all its swing power from the pivot-drive. In other words, the pivot-drive catapults/blasts the left arm off the chest wall towards impact. I believe that the left arm must start decelerating the further it gets away from the chest wall - because I know of no other force that can keep the left arm accelerating during the late downswing (near-impact) and during the post-impact followthrough phase of the swing.
Here is a graph from the TPI researchers showing that the left arm decelerates prior to impact.
Here is a photo from the Nike commercial swing video of Tiger Woods swing (taken at 4,000 frames/second).
Each white dot (showing the left hand motion) represents 1/400th of a second. The white dots gets closer together just prior to impact - which suggests that the left arm slows down slightly prior to impact.
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