On September 10th, 2011, "King" Muhammed Lawal knocked out Roger Gracie and was awarded the official knockout win by the commission-appointed referee. Unfortunately, as you will see in animated GIFs after the jump, said KO was most likely the direct result of an illegal unintentional clashing of heads that the referee failed to notice and take the proper actions to correct.
Here are the GIFs:
Some would say that since the referee failed to notice the illegal move it's impossible to go back in time and undo the official's mistake and know what the outcome could have been. For all we know, after a brief stop in the action Roger may have chosen to continue and this could have drastically altered the fight's course, or maybe he'd decide that he couldn't continue and it would have been a disqualification. Hell, Gracie could have chosen to continue and the result may have been the same as what we have. So one side of the argument would be that we should just go with the result we have even if it's not perfect because it isn't the fighter's fault that the referee didn't intervene.
However, precedent has been set for this kind of situation, quite recently in fact.
At UFC on Versus 4 on June 26, 2011, Charles Oliveira fought Nik Lentz, was lighting him up, threw an illegal knee when Lentz was on his way up off the ground and then stopped getting up. The referee inexplicably did not stop the action, the fight continued and Oliveira won by TKO not too long after. He was awarded a controversial win in the cage that night. Days later, the Pennsylvania State Athletic Commission decided to overturn the win and make it a No Contest retroactively because the referee failed to stop the action and penalize Oliveira for his illegal strike.
I personally disagreed with the retroactive overturning for the same reasons I outlined above, but it happened. If we're going to take away wins after the fact for illegal moves that weren't noticed by referees, we should do it across the board. Therefore, King Mo Lawal's victory over Roger Gracie should retroactively be ruled a No Contest.