Young Witch is a special case though. It adds a special ability to a card that didn't have it before.
No, it doesn't. That's like saying in game with Explorer, Province should include a clause that says, "If you reveal this when you play an Explorer, gain a Gold instead of a Silver." The bane card is just the same as it ever was. It's Young Witch that specifies the interaction.
Thing is, Province is already there. The bane is only there because Young Witch makes it appear. I mean, it's only a minor part of the bane, but it's still the whole reason for it's presence in the game. On top of that, Province is the same every game. When Explorer's out, well, you know Province can be used for that. When Young Witch is out, well, this game it's Hamlet, next game it's Cellar, game after that it's Watchtower, then Fishing Village, then Pawn...
I do see where you're coming from. But you definitely need some clear way of distinguishing 'the bane' card, and the bane only being recorded on YW isn't really clear enough.