This Henle edition is full of mistakes! We can freely admit this, because the odd notes here all come from Mozart himself – he consciously inserted them into his Musical Joke. in this amusing and mischievous piece, Mozart does not chiefly parody musicians who play wrong notes (the later title "Village Musicians" was not his). Rather, in this chamber music joke he aims an angry side-swipe at dilettante composer-colleagues of his time, whose lack of imagination and artless compositional technique are here mercilessly demonstrated. A musical and intellectual delight for today's performers and audiences alike!
Note: The "basso" role can be played by a cello, a bass, or both. This is disucussed in the preface to the edition.