Mozart?s concerto actually began life as a concerto for basset horn (not basset clarinet) and was written in the key of G. The manuscript ended abruptly after the 191st measure of the first movement. Mozart rethought his plan, decided to recast the concerto in A, and overhauled the solo part for basset clarinet, an instrument developed by his friend Anton Stadler The version that entered the repertoire after Mozart?s death was an adaptation of the original.