If I remember correctly, Rice's win on appeal simply vacated a revised suspension when the NFL suspended him for 2 games, which was their standard punishment for first time offenders at the time the DV incident happened, then later on they tried to re-suspend him a second time (indefinitely) for the same incident using their new policies which were put in place after the incident. The courts said you cannot change the policies after the fact and then try to re-apply them to an incident that happened before those changes were implemented.
So, in this case, the NFL cannot turn around and suspend Elliott for more than 6 games for the alleged incident against Thompson because 6 games is their standard policy now for first time DV offenders. However, since they closed the case against him on the shirt-pulled-down incident, they have not suspended him for that yet. There are no rules that prevent them from re-opening a closed case (not a legal term in this situation, it's just a word to say they are no longer investigating an incident) and suspending a player if they believe it violated their policies at the time of the incident.
That said, all the NFL would have to do is vacate the current 6-game suspension and then suspend him 2-games for the shirt-pulled-down incident. By vacating the first suspension, the second incident would then be the first ruling against Elliott as the other incident would no longer exist. Before anyone starts up with the already posted "she allowed it so it doesn't count" arguments, remember .. this is not criminal law .. this is the NFL deciding what constitutes "conduct detrimental to the league."
Again, I am not supporting the NFL's argument. I fully believe their best move is to admit mistakes, maybe fire one or two people for those mistakes, then drop the suspension and move on as fast as they can.