An investigation by the New York Times says at least 100 concussions - about 10 percent - were left out of a report from the NFL.
That report was done 13 years ago, and the league said it was a full accounting of all the concussions diagnosed by team doctors from 1996 to 2001.
Of those 100 missing, four are to Dallas Cowboys quarterback Troy Aikman. This despite his concussions had been made public on NFL injury reports.
The league's data doesn't include any concussions at all for the Cowboys more than a six-season span.
The NFL has been using their report as scientific evidence concussions don't cause long-term injury.
League officials now say teams weren't required to report every concussion.
Report: NFL concussion data flawed
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