The Sonata in F major bears two Koecher numbers: 494 and 533. The reason is that the third movement (Rondo) was written as a separate piece, a couple of years before the other two movements. The latter were composed in January 1788. It seems that the reasons why Mozart was forced to add two movements and form a sonata were mainly financial. Here is what Einstein has to say:
"... He [ie Mozart] owed his friend and publisher Hoffmeister money at the time, and doubtless partly acquitted the debt with this sonata. In doing so he paid no attention to what is called unity of style. These movements composed later have a grandeur of harmonic and polyphonic conception, a depth of feeling, and a harmonic daring such as we find only in his last works; indeed they are conceived for an entirely different and more powerful instrument than the innocent rondo, which is written mostly for the middle register. Yet even this rondo, with its lovely minore in three obbligato parts, is so rich and perfect that no uninitiated listener would observe any break in style."
Here is the Sonata in F major K. 494/533, with Zoltan Kocsis.