The issue is we're not talking about calcification in the bones. We're talking about the brain. Can the brain calcify? As much as I like using the term "bone-headed" I don't think it has any literal value with respect to resilience against knockouts.
You think it could work like bone hardening? I can punch a brick wall with some force behind it and not really feel it because I've been punching walls for a long time now.
Maybe you just tap your chin and hit it a bit everyday and maybe.. I dunno I'm curious.
It seems that resilience can be trained insofar as combat reflexes can be trained (one can be trained to go for a shot in response to eating a hard punch; or to throw a counter punch) but the force is still exerted on the brain.
I suppose one could attempt to calcify the skull, but somehow, I don't think it works that way. Is there an M.D. on the board who could clear that up for me?