A punished player may have received their punishment from multiple reports. The pop up message only appears to one of the players who reported them or so I have read and I've come to believe.
I will not name names, player positions, the outcome of the game, or selected champions for the sake of maintaining the anonymity of one case, but I will tell you that a player in one of my games recently continuously flamed one specific ally all throughout a normal draft game and claimed that they could fill that position better. When the game ended, the player filled the chat with obscenities about how we had reported them. No one in the chat said anything about reporting the player, but I had reported the player. The only way the player would have known is if they had received a punishment within that time and punishments are usually issued shortly after reports are sent.
People complain that an automated system is flawed, but with hundreds of thousands, if not millions, of players playing every month in NA alone, the Tribunal had proven ineffective with its members automatically clicking the punish option without bothering to review cases. It had been replaced by an automated system that generally issues punishments to those that fill chat to the brim with offensive language.
Punished players can contact Riot personally for an appeal, but the players who receive their punishments are usually found deserving of them.
We don't need to know who was punished when and why. That little pop up message you long to see in your client is nothing more than a courtesy Riot extends to the community to show the system is working.