An alternative version found in Go.S.19 also stemmed from the lost autograph, which contains many variants (some of which look as if they were conjecture). I have deliberately left the original pitch errors found in the copy in this MIDI sequence .
Bach's autograph for this movement does not survive. The 'London autograph' is copied by Anna Magdalena, who copied from the autograph. Her exemplar was presumably a revision score in which Bach extended the piece from 43 to 53 bars long .
Bach later decided to extend the piece by inserting two extensions into the 'London autograph'. The final version is 61 bars long. At this phase of the revision, Bach also enhanced the metric character of the piece .