I watched it today with my son who hasn't seen any of them, and that was the only reason it was so fresh. I always thought the planet was Hoth, but then heard the lines from Vader... "Hoth system" "sixth planet"... Why would the sixth planet have the same name as the star it orbits? It seems to have been a simplification on the back end, because if it is unnamed, people would have to say "sixth planet in the Hoth system" every time they talked about it, and as the star it orbits is really of little consequence to the story, the planet is called Hoth and through general use it is accepted over time.