If you are seriously denying that people in the 90s didnt know about head trauma then this conversation should be over. I mean Stevens himself suffered from a delayed concussion in 94.
I think people understood that a concussion (very obvious symptoms) was indeed serious, but what wasn't know, due to changes in diagnostic methods thanks to medical advances, was how early the damage starts (asymptomatic), that the damage is cumulative, and how to diagnose players.
As the evidence mounted and you started seeing players dying off in their 40s due to degeneration of the brain and neurological function, people studied the issue further. We know much more today than 20-30 yrs ago.
I'm not interested with arguing semantics with you; it's clear to anyone who has been following the sport since the 90s (or sports in general) that concussions are taken far more seriously today - back then, taking out a player's knees was considered far more serious.
I think this is true since it was immediately obvious that the knee was done, career over. Getting your bell rung didn't connote the same medical impression then as it does today.
Further to that, medically more things are possible today than in earlier eras, so the same kind of knee injury didn't necessarily mean the end to one's career.