A long accent could have been added in the penultimate stage of proofreading of FE; it is indicated by the absence of the mark in EE along with the shift of dim. – see the previous note. In GE the mark was almost certainly erroneously interpreted as a 
hairpin.
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category imprint: Differences between sources; Corrections & alterations
issues: Long accents, Inaccuracies in GE, Authentic corrections of FE
notation: Articulation, Accents, Hairpins