I've never quite understood why people are reluctant to listen to "completed" works on the grounds that they are not the total work of the original composer, whether this be Mahler's 10th, Elgar-Payne 3rd, Mozart's Requiem, Schubert's completed 7th, 8th & 10th, Bruckner's 9th or Puccini's Turandot. Is it better to pretend the music doesn't exist, or is it better to hear another musician's/composer's idea of how it might have been? Provided that no attempt is made to deceive the listener, it hardly matters who wrote it.
Consider Jeremiah Clarke's "The Prince of Denmark's March". Does it matter that it was composed by a lesser composer than Purcell (to whom it was once attributed)? Or the Minuet in G formerly attributed to Bach, but now thought to be by Petzold? How much does the name on the top right-hand corner of the music really matter. Surely, it's what the person sitting/standing in front of the music produces that matters.
Agreed, and then there's the thorny issue of BWV 565.