'Shell shock' is an obsolete term originating in the First World War (1914-1918) and referring indeterminately to either PTSD secondary to war trauma, or the chronic traumatic encephalopathy to which you refer. The term's imprecision is why it was retired.

I recall the bit well, and being struck as much by its insistence on direct and meaningful language as by the fierce sort of kindness he made evident in its ending. Carlin was and is a treasure. But if I get treated for PTSD when what I have is CTE or vice versa, I probably won't do so well. In that sense, the more specific modern terms do have value, jargon though they also be.