The logic and idea of a jam is to make a game within the specified timeframe(from start of the jam to the end), within a specified theme and specified constraint. If you have a game applying to multiple jams, most likely it is not being made within the specified timeframe and constraint. That is not participating the jam, this is just trying for free advertisement. I do agree that it’s up to the jam hosts/organizers to enforce the rules, but multi-jam entries are completely against the entire spirit of a jam-game.