b. 686
The version of FE is almost certainly erroneous, in spite of the fact that it was proofread; originally, in FE this bar was identical to the next one, yet it was only the 3rd note that was corrected, perhaps due to misunderstanding Chopin's proof entry or due to an incomplete implementation of the proofreading. EE repeated the version of FE from before proofreading, which, unless it is an extraordinary coincidence, means that it was a change introduced in the last phase of proofreading.
Compare the passage in the sources»
category imprint: Differences between sources
issues: Errors in FE, Authentic corrections of FE, Partial corrections
notation: Pitch