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b. 17

composition: Op. 28 No. 16, Prelude in B♭ minor

f in chord in A (→FEEE)

e in FC (→GE)

..

The second note from the bottom of the L.H. chord was written in FC imprecisely, hence it looks more like e rather than f.

category imprint: Graphic ambiguousness; Differences between sources

issues: Inaccuracies in FC

b. 17

composition: Op. 28 No. 16, Prelude in B♭ minor

..

In the main text we include the cautionary  before a2, added in FE (→EE) and GE.

category imprint: Differences between sources; Editorial revisions

issues: GE revisions , FE revisions

b. 20

composition: Op. 28 No. 16, Prelude in B♭ minor

..

Chopin wrote a cautionary  before a3 at the beginning of the bar. In the main text, we also add a  before the next note, g3.

category imprint: Editorial revisions; Source & stylistic information

issues: Cautionary accidentals

b. 22-23

composition: Op. 28 No. 16, Prelude in B♭ minor

b1 & b2 in A & FE2 (→EE)

b1 & b2 in FC (→GE)

b1 & b2 in FE1

..

Before the 7th semiquaver in A there was initially a  (cautionary due to B(1) in the L.H.), which Chopin turned to a . Fontana and the engraver of FE1 misinterpreted that correction by considering it a deletion of the accidental, hence FC (→GE) and FE1 does not contain any accidental before that note, which gives b1. When the figure is repeated an octave higher (at the beginning of b. 23) in FC (→GE), there is also no , which can be explained by an oversight (it would be a puzzling coincidence!) or by a revision, introduced in the belief that it is also here that the alleged crossing-out from b. 22 should be taken into account.
In both places, the naturals visible over the notes were added in FC by H. Scholtz probably in the 1870s.

category imprint: Differences between sources; Corrections & alterations; Source & stylistic information

issues: Corrections in A , Errors resulting from corrections , FE revisions , Errors of FC

b. 22

composition: Op. 28 No. 16, Prelude in B♭ minor

..

In A there was initially a  before the 5th semiquaver, which, together with the  before the 7th note, would result in the following sequence, in which the 5th, 8th and 10th notes would be c2.
In the next bar, when the subsequent seven semiquavers (counting from g1) are repeated an octave higher, there are no traces of changes – the final version was entered straight away.

category imprint: Corrections & alterations; Source & stylistic information

issues: Corrections in A , Deletions in A , Main-line changes