Chopin entered slentando into FC (→GE). Similarly, Chopin added the smorz. - - indication present in FE (→EE) probably only just while proofreading this edition.
Therefore, both indications, of a similar meaning, can be regarded as equal variants.
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category imprint: Differences between sources; Corrections & alterations; Source & stylistic information
issues: Authentic corrections of FE, Authentic corrections of FC
notation: Verbal indications