In Pokémon D/P/PT, and HG/SS, you can create a Social Group in Jubilife City, or Violet City. While it may seem like a useless feature, it's actually very helpful: it synchronizes certain event types if you're in the same group as someone you mixed records with! For example, swarms, Feebas tiles, the Pokémon Lottery, and a few other mild things.
Did you make a Group in D/P/PT? If so, what did you name it? I honestly didn't know that groups actually DID something in the games. I just thought they were a cute little nothing feature that served no purpose in the game.