That would just add unnecessary "But the TV show says this and it's more recent that the game so it's right" arguments.Honestly, I feel a series based on the games/manga would just be a retread. I'd prefer some sort of anthology. Some nice shorts that add to the series by going more into some characters. Like Lea and Isa's lives in Radiant Garden or Kairi's life during the year everyone forgot about Sora. Stuff like that.
Also, consider the viewing audience. If it were shorts giving insights to characters and events the audience is suppose to know, that show will be cancelled really quickly from low ratings because it would be hard to watch if you're not that familiar.
Making it a "retread" would still get the younger audience to watch, since parents might prefer their child to watch a cute show with mixing Disney characters rather than them playing a game.