The flat lowering a3 to a
3 is only in GE and EE. Lack of the sign in the remaining sources is an inaccuracy of notation, characteristic for Chopin.
Compare the passage in the sources »
category imprint: Interpretations within context; Differences between sources
issues: EE revisions, Accidentals in different octaves, GE revisions, Inaccuracies in A, Errors repeated in FE
notation: Pitch