Chopin most probably added 
in bars 40 and 50 only just in [A], after AI had already been prepared. It is uncertain if the shift of both marks from the 1st to the 2nd beat of the bar performed in the stage of proofreading FE2 (→EE) was a correction of a misinterpretation of the [A] notation or a change of concept. The fact that Chopin bothered correcting such a small difference suggests that it could have been a more significant change, and not only keeping 
on the 1st beat of bars 40 and 50. at the beginning of the bars almost certainly indicates 3-bar segments performed forte (bars 40-42 and 50-52). On the other hand, the same marks placed directly before chords could be interpreted as, e.g. referring only to the pair of chords in each of these 6 bars.
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category imprint: Differences between sources; Corrections & alterations
issues: Authentic corrections of FE
notation: Verbal indications