The original recording seems to be from a rehearsal/sound check and there seem to be some quiet vocals on it toward the end. I think Neil heard those later and decided such understated vocals made the instrumental tracks more interesting so he dubbed vocals over them later and ?that was what is on the initial releases. Then he changed his mind and probably thought it was not authentic enough because they were also not like that in the film. I actually think they are more interesting like that!
Robert (Broadfoot) - Dirigible Dan