From what you say, it's just the NECK that is numb, correct? There is no numbness in the limbs?
It would seem to me that with all the surgery that was done, you sustained some nerve damage, causing this numbness. If there's no pain/burning with it, I wouldn't worry too much albeit I'm sure it's annoying.
I have some of the same, only in the lumbar area. I've been 'opened' there twice, and then had a spinal cord stimulator put in besides -- then removed. So I have some numbness along that area too.
I hope it isn't causing you any trouble and I hope your surgery days are over. Best of luck and God bless. Hugs, Lee