The fourth draft wasn't used to shoot any of the film. It was written months before production began. A new draft was penned just before shooting. The fourth draft is the fourth draft, not a shooting script. And it goes out the window even on Hoth--theres different scenes of the rebel P.A announcers fighting Imperials and many different such scenes. Productions don't use one draft to shoot one section of the film and then another draft to shoot another section--if theres stuff in the fourth draft that they liked then thats carried over into the next one. But keep clutching at those straws.