At 15, Wolfgang Amadeus Mozart was commissioned to provide music for a royal wedding in Milan. He offered the dramatic vocal work ''Ascanio in Alba" and musical accompaniment for a ballet to be danced between its two acts. The 1771 premiere was well-received, a repeat performance was demanded two days later, and then, incredibly, the score of the intermission music simply disappeared, the only trace of it a copy of a version for piano made sometime in the 1930s.
This matter was considered closed until the Australian musicologist Ron Hunter studied that sketch, thought about the sort of orchestra available in Milan, and reconstituted the ballet music for performance by the Handel and Haydn Society, bringing about a new Mozart piece just in time for the composer's 250th birthday celebrations.