In A there is no cautionary 
before b1 at the beginning of the bar. It could be considered as an argument for b1(2) in the previous bar, since the cautionary 
before the next note (c2) is written in A. However, the situation is even more complicated by the fact of deleting a sign before the 1st note – if it was a flat, it would suggest that Chopin had heard b1. Nevertheless, there would be no reason then to remove the sign. In any case, in a proofreading of FE a was eventually added, probably during the last proofreading of FE (→EE), as it is absent in GE1. The sign was already added in GE2 (→GE3→GE4), while in GE3 (→GE4) a before b2, the 4th semiquaver, was also added.
Compare the passage in the sources »
category imprint: Differences between sources
issues: GE revisions, Cautionary accidentals, Authentic corrections of FE
notation: Pitch