Fair enough.
Personally, I don't believe CE 399 has anything to do with the actual shooting.
If the argument is the bullet couldn't have hit the spine because CE 399 was unblemished then I'm more inclined to think the bullet did pass between the C-7 and T-1 process, and this caused the fracture and that he bullet that did this fragmented on JBC's wrist.
The Magic Bullet is garbage because it relies on CE 399
The Single Bullet is just a bullet - not CE 399. A bullet passing through both men is not really that big a stretch. It is if you believe that bullet was CE 399
If CE 399 was planted then how could the planters know beforehand how many other bullets (or fragments) would be recovered? How could they have known that CE 399 would not be the "one bullet too many" that would blow the whole plot? And they planted it on a hospital gurney? They were awfully lucky that it was found.
This entire aspect of their plan (if there was one) is an enormous risk. One that makes no sense to me. Too many things to easily go wrong; too many things to have to control; too many moving parts. That doesn't prove it didn't happen; it just makes it seem very odd to me.
Second: I don't see how a bullet could strike JC in the location that it did and at (roughly) the time on the Z film that I think it did and not go through JFK. Kennedy is blocking the view for a sniper. It's impossible, as I see it, for a sniper to hit JC in the back. A sniper's view is blocked. Even if there was a second sniper then where could he have been located? It seems to me that the evidence tracing a bullet backwards would have two men in the sniper's nest? Or very close by.
If you look at the alternative explanations for the wounds on JC they make no sense to me (the bullet that struck JC's thigh, according to his doctor, barely penetrated the skin: so what happened to it?). Which leaves us with the best explanation available: one bullet hitting both men.