Back wound was from a sub sonic round used by sniper to reduce noise, and making the through and through back shot to leave a small exit hole as slug hit nothing hard to distort slug making a big exit hole.
Your conclusions are consistently among the goofiest presented in this forum. You are correct that CE399 did not deform because upon hitting soft tissue but that is because it was a FMJ bullet that is designed specifically not to deform upon hitting soft tissue. That is the reason the exit wound in JFK's throat was a neat, round hole, but your explanation that it was a sub-sonic round is bizarre. Why would an assassin resort to using such an underpowered round. It makes no sense.