Franchomme described the variant of the Nocturne opening that he gave in FEFr as „the change made by the author”. However, his version is not free from inaccuracies. A flat instead of f as the last semiquaver note of each group is certainly erroneous (Franchomme made the same mistake twice more, notating a variant of bar 28 in FEFr). The note D flat at the beginning of the second bar of the variant is also doubtful. In a similar context, shifting the bass down an octave often appears only once in Chopin's works, at the beginning of the harmony - cf. bars 1-4 of this Nocturne in its main version or bars 81-86 of the Sonata in B op. 35, mvt. II. The original Chopin's notation of that variant was probably in the form of an abbreviation (‘bis’ or ∕∕); use of such abbreviations often resulted in mistakes in the score (autographs of the Impromptu in C sharp WN 46, bar 121, or Sonata in B op. 58, mvt. IV, bar 177). Bearing all that in mind, the following execution of the variant seems admissible: 
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category imprint: Differences between sources
issues: Annotations in FEFr, Authentic post-publication changes and variants
notation: Rhythm