Recently I have studied several revisions of important symphonic works, the Third and Eighth Bruckner Symphonies and the "Little Russian" Symphony #2 of Tschaikovsky from recordings with orchestral scores. This is a window into the creative process at the mid level of scale. At the lowest level is the most difficult, the least tangable, or creation of motives, themes, melody and phrases, like composing sentences in language. Above that in the relm of these kinds of works are two different tasks. The first is to expand smaller musical ideas into the process of the larger form. What these revisions show, often separated by a decade or more in time is how each composer masters form as he matures. It is at once clear that the outer movements of four movement symohonies present the most challenge and that inner movements such as adagio or scherzo have more to do with the second main task or orchestration.
To be sure the Adagio of Bruckner Third from 1873 was reworked at least three times. First, there is the change caused by Wagner's death wich caused the composer to alter the coda of the movement, that is historical, but there or the numerous textual changes, such as the elimination of the counterpoint in the high voices (violins) between the 1873 and 1889 versions, but even with the common cuts Bruckner made, the work was not reworked as much as the outer movements.
The same can be said for the inner movements of the "Little Russian". They are less changed between the earlier version and the later one, although the Scherzo is textually reworked, the same sound is there and the orchestration has been changed. In fact I think that the older version is rhetorically clearer than the newer one. The syncopation and motion of the bass line is clearer than in the later version. The second movement is least changed.
The real struggle concerns the form and text of the first and last movements of the Bruckner Third Symphony. It is obvious to the casual listener that the later (1889) version, the one which is usually performed, flows better, especially in the last movement. Bruckner seems to have relied on bringing things to a screeching halt as a younger composer to create points of arrival within the sonata form, and then to have tightened up overall form considerably in the later version, which was made after the success of his Seventh Symphony. That it is the form which makes the difference is clear since thematic material was not changed very much.
Now, the Eighth Symphony also has two versions, but the differences come mostly from cuts in the outer movements and more changes in the scherzo, which suffered more recomposing. My opinion is that on some days I like the new better than the old and on other days the reverse.
