In A (→FE→GE), there is no accidental to the 4th L.H. crotchet. Chopin's patent, as it seems, oversight went unnoticed by FE and the majority of GE; it was corrected only by EE and GE1a.
In A, the L.H. part was being corrected in this bar; consequently, due to deletions, Chopin was forced to write the final version on an adjacent stave. However, the flat was not overlooked due to the corrections, since it was also absent in the initial version of notation. The change concerned mainly rhythm, i.e. there were rests instead of the 3rd and 6th crotchets: 
. Before deleting the entire bar, Chopin probably changed the last chord too: 
(both examples are to be interpreted in the key of E
major, featuring A and a notes).
Compare the passage in the sources »
category imprint: Interpretations within context; Differences between sources; Corrections & alterations; Source & stylistic information
issues: EE revisions, Corrections in A, GE revisions, Deletions in A, Accompaniment changes, Inaccuracies in A, Errors repeated in GE, Errors repeated in FE
notation: Pitch