Disregarding certain details that do not affect the sound, the accompaniment in that bar has two authentic versions :
- the earlier one, recorded in A and reproduced in GE and EE3; this version is consistent with Chopin's only version of the analogous bars 50 and 112;
- the later one, introduced by Chopin during the proofing of FE (→EE1→EE2).
The first version is written out buy Chopin thrice, and therefore does not give rise to any source-related or stylistic doubts. The authenticity of the second version is also hardly questionable, even allowing for the possibility that some misunderstanding occurred in the course of Chopin's proofing of FE. This, however, does not necessarily have to mean that Chopin changed the version of A (→GE); when proofing FE he could have before him the text of that version printed with errors. That issue is linked to a vital question about the relationship of bar 18 with its repetitions in bars 50 and 112. As all the three bars had identical text at the stage of writing A, perhaps when changing the version of bar 18 Chopin intentionally corrected the remaining two bars as well? In our opinion this is rather unlikely, as the context of bar 18 is different from that in bars 50 and 112. The composer's intention could be to find the way to vary the version of that bar in relation to its repetitions. From the point of view of harmony, the version of FE is slightly less tense - the adding of a seventh mellows the sound effect of the octave a flat2-a flat3 in bar 19. Cf. the note to bars 18-19.
It is difficult to find any explanation for the 
before c1 visible in A on the 3rd beat of the bar.
Compare the passage in the sources »
category imprint: Differences between sources; Corrections & alterations
issues: EE revisions, Cautionary accidentals, Accompaniment changes, Authentic corrections of FE
notation: Pitch