We perceive the indication 
in bar 50, added by Chopin in the three teaching copies and written into FEFr, to be part of a definitive change of the dynamic concept in several fragments of the Nocturne (cf. bars 25-26, 45-46, 52). The 
noted by Franchomme in FEFr naturally supplements that change.
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category imprint: Differences between sources; Corrections & alterations
issues: Annotations in teaching copies, Annotations in FED, Annotations in FES, Annotations in FEFr, Authentic post-publication changes and variants, Annotations in FEJ
notation: Verbal indications