Take the classic "shell shock" bit. Carlin defines it at "a condition in combat that occurs when a soldier is completely stressed out and is on the verge of a nervous collapse." However, that is not the WWI definition. Quoting https://ajp.psychiatryonline.org/doi/full/10.1176/appi.ajp.2... :
"The term “shell shock” evolved in an attempt to describe cases that arose in the context of exploding ordnance but where enduring symptoms could not be linked to the presence of an obvious organic lesion."
The problem was, from the same link, "many shell-shocked soldiers had been nowhere near an explosion but had identical symptoms to those who had. ... when it had become clear that many cases of shell shock were not directly related to a head injury, military medical authorities attempted to restrict use of the diagnosis. Servicemen invalided from the front were given a preliminary label of “not yet diagnosed, nervous,” and those who failed to recover but had no visible cerebral injury were then classified as “neurasthenic.” Disputes over the etiology and management of shell shock served to inhibit further the design of an effective protocol."
This should be very familiar to those who remember the PTSD debate in the post-Vietnam era.
So when Carlin say "I’ll bet if they had still been calling it 'shell shock,' some of those Vietnam veterans might have received the attention they needed.", I don't really think that's true.
We can even read of some of the attention received by WWI victims of shell shock, at https://en.wikipedia.org/wiki/Shell_shock :
"Some men with shell shock were put on trial, and even executed, for military crimes including desertion and cowardice.[16] While it was recognised that the stresses of war could cause men to break down, a lasting episode was likely to be seen as symptomatic of an underlying lack of character ... The continued pressure to avoid medical recognition of shell shock meant that it was not, in itself, considered an admissible defence. Although some doctors or medics did take procedure to try to cure soldiers' shell shock, it was first done in a brutal way. ... a patient who had, over the course of 9 months, been subjected unsuccessfully to numerous treatments for his mutism; these included strong application of electricity to his throat, lit cigarette ends applied to the tip of his tongue, and "hot plates" placed in the back of his mouth"
PTSD is a larger category which would include shell shock, but also includes (as the VA point out at https://www.research.va.gov/topics/ptsd.cfm) military sexual trauma, which wouldn't be classified as "shell shock" but has similar symptoms and treatments.