The use of the 
time signature is surprising only in EE, as in FE the 
time signature was not used in the Etudes even once – contrary to the manuscripts – neither in Op. 25 nor in Op. 10, in the Etude in F minor, Dbop. 36 No. 1 (cf. the Impromptu in A
major, Op. 29). Anyways, the correctness and authenticity of the time signature written by Chopin in A (→GE) is beyond any doubt.
Compare the passage in the sources »
category imprint: Differences between sources
issues: Changes of metre, Inaccuracies in FE, 4/4 or 2/2
notation: Rhythm