Yeah, Seiken Densetsu sounds right.

Square wasnt careless, they were thinking logically. FF already had a fan base, albeit a small one. So they could either a) market the game by its original name, in a time when RPGs werent at all mainstream or b) market it by an FF name, which gave it at least a fighting chance. Although it is annoying the way Square screwed up the names and numbers, I can easily see their reasoning.