I’m thinking of the music that plays while Luke is lost in the snow, and while the film cuts to the Echo Base and a new piece comes in, the score alone carries on. I just always remember it because they used it in the Shadows of the Empire game soundtrack.
There’s a lot of music from Empire that was cut out, particularly at the beginning (and in some cases new pieces were recorded instead). But the intention originally was in fact to include that music in the film.
Two tracks were dumped in favor of other tracks. The search for Han and Luke has the Hyperspace track from the end of the film instead of what was written for it. And the concert version of the Imperial March was used for the reveal of the SSD instead of the track written for it. Like everything else, it is a matter of having the right music and sometimes what a composer comes up with and records is not what works best.