Personally, I believe the NFL did try to conceal this info. Fascinating article so read the link.
The National Football League conducted a two-decade campaign to deny a growing body of scientific research that showed a link between playing football and brain damage, according to an excerpt from a new book co-authored by a pair of ESPN investigative reporters/quote]
• The league in 2005 tried unsuccessfully to have medical journals retract the published work of several independent concussion researchers.
• Independent researchers directly warned Goodell about the connection between football and brain damage in 2007, but the commissioner waited nearly three years to acknowledge the link and to dismantle the league's discredited concussion committee./quote]
Click here for link