I believe the bullet that passed through JFK and hit JBC in the back is the one shown just behind the reenactor's right ear by the hairline.
The shot to JFK's back, apparently, did not penetrate more than an inch or two.
Sometime after this reenactment by the SS, it was decided that the wound by the hairline should be forgotten, and that the back shot show now be connected to a throat exit - which as you can see from the below photo and considering the sixth floor snipers nest behind - is preposterous. But, without dropping the hairline shot, you've got three hits on JFK...and that just doesn't work well with the lone nut scenario...
https://photos.google.com/search/_tra_/photo/AF1QipOgAYwTqNlIRPDhDbLL_gZEIor5ooWadb8WxfV-