Of course the neck wound looked like an entrance because of the subsonic round fired. Was it an entrance, NO!
It had to be an entrance wound because the back wound had no exit point, because the back wound was too low to have exited the throat anyway unless JFK had been leaning forward by nearly 60 degrees, because there was no hole through JFK's tie (as there would have been if a bullet had exited the shirt slits), and because the nick on the tie knot was not on the edge of the knot (and we have ample photographic evidence that JFK's tie knot was neatly centered in the middle of the collar band before and during the motorcade).
The SBT died when we learned there was no hole through JFK's tie, neither through the knot nor through any part of the rest of the tie. The tie knot was directly over the shirt slits. Any bullet exiting those slits could not have avoided tearing through the tie, nor could any such bullet have magically performed like a guided missile and weaved around the body of the knot and nicked the top surface of the knot inward from the left edge. Not on this planet anyway.