Again you are speaking of MORROWIND haveing no indroil and dres. Vvaranaval DOES have it not to mention they could just have some leader of dres and indroil apear and give you a quest and if you succeed you become horator.
Dude, are you mixing up Morrowind and Vvardenfell? Vvardenfell is the island, Morrowind is the entire province which includes Vvardenfell and the mainland parts.
Besides, it doesn't even matter. Like I said, prophecies can be as particular and arbitrary as they like. If the prophecy says 3, then all it needs is 3. It could have just as easily been only 2, and the player would take their pick of the 3 Great Houses on Vvardenfell.