The traces of changes visible in FE prove that Chopin changed the enharmonic notation of the chord – c1 (with a cautionary 
) replaced the original b
1. The change was most probably followed by subsequent ones – the cautionary naturals before the c1 semiquaver in bar 436 and c2 in bar 437 were removed. All those accidentals are actually superfluous after bars 434-435; however, they prove that the B major key, present from bar 324, triggered the composer to clearly mark the return to the E minor key, beginning in the discussed bars.
Compare the passage in the sources»
category imprint: Corrections & alterations; Source & stylistic information
issues: Cautionary accidentals, Enharmonic corrections, Last key signature sign
notation: Pitch