A performer can do a lot with 'old' material, giving it new life, or new understanding.
Many people think that only 'as it is scored' performance is correct, but that means the performer should only be a mimic, not an interpreter. It seems that the 'Saints' has undergone many changes since its first incarnation; each one offers a different interpretation of the theme.

On the classical side, I especialy enjoy Bach's cello pieces; I have five recordings by different cellists, and each has something new or variant to add. Composers themselves often added variants to their compositions. The same process is important in all music.