In A one can see a crossing-out between the 
and the 3rd quaver. It was most probably the 
before a that was removed (superfluous), yet it seems that, for some reason, Chopin also crossed out the correctly written f
-a third, which he then reintroduced next to it. If it was so, the reason could have been, e.g. accidentally blurred noteheads, even partially, as a side effect of removing the natural.
Compare the passage in the sources »
category imprint: Corrections & alterations; Source & stylistic information
issues: Corrections in A, Deletions in A
notation: Pitch