The initial version of AsI and A, with only one a2-c3 third, was additionally depleted by GE (→FESB,EE1→EE2), which did not notice the a2 crotchet at the beginning of bar 291 (it can be difficult to establish the presence of a middle note on ledger lines in Chopin's autographs, although in this case the a2 notehead is quite distinct). While proofreading FE1 (→FE2) Chopin added bottom thirds to the entire three-note motif, which was also taken into account by EE3.
Compare the passage in the sources»
category imprint: Graphic ambiguousness; Differences between sources; Corrections & alterations
issues: Errors in GE, Authentic corrections of FE, Uncertain notes on ledger lines
notation: Pitch