This version is 17 bars long, and known through Bach's pupil's copies,
such as J. P. Kellner's P 804 (dated 1726) and J. C. Vogler's P
1089 (dated 1729). Its texture is much thinner and less consistent
than the later versions 
.
Vogler's version (with many more ornaments and fingerings) is also worth
studying, for it is highly likely that they were most likely written in
under Bach's supervision .
Based on the early version, Bach extended the piece in the 'London autograph'
from 17 to 34 bars.
Bach thickened the texture, while adding a lot of chromatic flavour .
Probably based on the 'London autograph' and reworked by W. F. Bach
for his own purpose.
Note the modified texture and further exploitation of chromatic passages.
Autograph is lost, but this version is reflected in the copy made by
J. C. Altnickol in 1744.
Note the introduction of demisemiquaver flourish and improved texture in
the first bridge (bars 14-19) .