In theory, better diagnostic tools should have led to more reported concussions, not fewer. The league said that having more doctors present on game days enabled them to more precisely determine when concussions had actually occurred. In previous years, diagnoses had been less precise, which led to a greater number of misdiagnosed concussions. “The increased scrutiny might have taken the numbers in a positive direction,” said Dr. Matthew Matava, the team physician of the St. Louis Rams and the president of the N.F.L. Physicians Society, referring to the decline in the number of concussions.

Other experts who study head trauma in sports disagreed. They said that better education and tests should significantly increase the number of reported concussions. The more fundamental problem, they said, is that players continue to try to hide concussions because they do not want to be removed from a game, put on the injured reserve list or cut from a roster.

“I commend the efforts that the N.F.L. and N.F.L. Players Association have made,” said Chris Nowinski, the executive director of the Sports Legacy Institute. “However, I’m still certain that 90 to 95 percent of concussions are still not diagnosed, so in that sense the numbers are meaningless. If you can diagnose every symptomatic blow to the head, you wouldn’t have enough players on the field.”

The league also said the average number of injuries on Sunday and Monday was slightly higher than on Thursday games this season.