Throw in the illegible handwriting of, say, a Beethoven, or a composer who makes changes on routinely tossed publisher's proofs but neglects to enter them on the original manuscript, as well as the inevitable errors endemic to the typesetting and printing process itself, and the vagaries of the score-publishing process become manifest.
WSJ: Ravel| Mother Goose| New York Philharmonic| Arbie Orenstein