Older quests should be playable in 2.50. I think minor differences are generally acceptable, especially in cases where the earlier versions didn't correctly match the NES game. If a quest is unwinnable or otherwise doesn't work as intended in some major way, that should be considered a bug. I'm not aware of any such problems at this point, but I won't be surprised if some turn up.
I'd say that's less true for quests made in earlier 2.50 builds, though, or at least the more recent ones. If it's basically a 2.50 quest anyway, I don't feel too bad about requiring it be updated.
