It is the longest out of three evident long accents written in A in bars 21, 25 and 27. In FE (→GE1,EE) it was reproduced as three-semiquaver-long 
hairpins. In subsequent GE, the sign was extended in order to cover the entire length of the semiquaver beam (such kind of adjustments of slurs and hairpins to regular rhythmic groups was a characteristic manner of German engravers, both Kistner and Breitkopf and Härtel). Cf. bar 27.
Compare the passage in the sources »
category imprint: Graphic ambiguousness; Differences between sources
issues: Long accents
notation: Articulation, Accents, Hairpins