I agree that there should be a rule requiring the game to be made during the game jam. Legitimate arguments about fairness and stuff aside, submitting from a backlog of older games just seems against the spirit of a game jam.
On that note, though, I did like that the theme was announced like 2 weeks before a 3 or 4 day submission period. That felt like a nice buffer to give people some wiggle room to work the jam into their schedules that wouldn't have been able to otherwise.