The problem is that sometimes, symptoms do not always show up right away and they're not always the same across each person. One person might have mild amnesia and confusion, balance issues, "got his bell rung" type symptoms where another might have headaches and problems focusing, etc. It's very possible that during OU, he wasn't having symptoms immediately after the hit and was cleared to go back in, and then started to develop symptoms later during the week. If they're mild symptoms, maybe he doesn't think much of it, doesn't report them, or maybe he tries to tough it out because that's the kind of player that Sam seems to be. Maybe this concussion is lingering from OU, maybe it got exacerbated during OSU, or maybe he never had a concussion and this is in fact truly entirely from the OSU game. I'm completely speculating and it's impossible to know. That being said, it's not impossible that he suffered a concussion during OU and was symptom free in the immediate aftermath, hence being cleared to go into the game.