Largo written in FES instead of Allegro, which was crossed out, is most probably a teaching correction – it indicates the way the piece should be practised, and not a change of concept of the Prelude. Placing the Prelude in E
Minor provided with Largo between the Preludes in F
Major and D Major (Lento and Sostenuto, respectively) seems to be unlikely due to the structure of the entire cycle.
Compare the passage in the sources »
category imprint: Differences between sources; Corrections & alterations
issues: Annotations in teaching copies, Annotations in FES, Authentic post-publication changes and variants
notation: Verbal indications