written into 
in Having already published the Nocturne, Chopin apparently changed his concept of dynamics for the returns of the main theme. This finds proof in identical corrections made in all the three extant teaching copies, both in this and the previous bar. There are even more radical changes notated, with similar determination, on the 3rd appearance of the theme in bars 45-46 and 50 & 52.
The additions and alterations notated by Franchomme in FEFr seem to define - despite certain differences - a very similar change of dynamic concept, here and on the 3rd return of the theme.
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category imprint: Differences between sources; Corrections & alterations
issues: Authentic post-publication changes and variants
notation: Verbal indications