I was recently talking with a neurosurgery fellow who claimed CTE is a bit of a controversial diagnosis to begin with. Not only can it only be diagnosed posthumously, but it cannot be diagnosed by autopsy alone. According to him, many brains display the pathology characteristic of CTE. What makes it CTE or not is a history of concussive/subconcussive injuries.

Of course, I may have misunderstood him and/or his opinion may not be in sync with the consensus in the field. Still, it's not something I've heard in these discussions.