The City of Birmingham Symphony Orchestra's celebration of Mozart coincided with the anniversary of his death, but 215 years on, he might have been turning in his grave with the knowledge that someone had attempted to finish what he had left incomplete.

While the story of his Requiem fuels the Mozart legend, the unfinished state of his Mass in C minor - performed in part in Salzburg in 1783 - is less familiar. There have been previous attempts to fill the gaps but, for the American scholar Robert Levin, the temptation to provide a new solution was irresistible, though it is mainly a question of reverse recycling.

If Mozart himself re-used music from the C minor Mass for the cantata Davidde Penitente - also unfinished - then why not use material from that cantata as polyphonic filler? Levin is famously adept at DIY Mozart: he improvises brilliant cadenzas to the piano concertos, and his completion of the Requiem will have been heard frequently in this Mozart year.

However, anyone can hear the joins in this Mass and, for all Levin's facility in spinning out the counterpoint, it doesn't quite ring true, least of all the final Dona Nobis Pacem. The CBS chorus gave conductor Charles Mackerras their customary best, but that in itself was not enough.

Prime reasons for celebrating Mozart's original music are the solo numbers: Rosemary Joshua's Et Incarnatus, and her Domine Deus duet with Sarah Fox were wonderfully expressive here.

Since these solos were inspired by the lovely voices of the Weber sisters, it is touching to think that two of them were at his deathbed. Such sentiment is dangerous, however, and risks over-validating experiments like this, which Mozart would have left, and did leave, well alone.