NOTATIO

A controversy surrounds a note In measure 7 of Chopin's Etude op. 10 no. 6. (measure 3 in the first example which is from the composer's autograph.)

Should it be a C flat as in Chopin's autograph and the French first edition, or should it be C natural as in the first German edition and in most editions since. After all, C natural is what one expects in a such a cadence. Might this be an error in the autograph or one of Chopin's corrections after the fact? Or is it an engraver-editor correction?
Questions of this type come up frequently in music editing, and if the primary sources are in conflict, critical editions can only present the situation for the reader to consider. However, I think that internal evidence can sometimes lead to a definitive or at least probable conclusion if one looks below the surface. In this case, it think it highly probable that what Chopin wrote in his autograph is correct and that most performances of this piece are marred by a wrong note..

To understand my case, one must first understand the harmony in question. As in many such cases of "altered" chords, a note is omitted, in this case the C natural, because it is mentally supplied by the context, leaving behind a chromatic passing note that connects to a foliowing note, in this case, the B flat.
Apparently, Chopin needed the passing note C flat, but didn’t want both the C natural and the C flat in the alto voice for rhythmic reasons. So why was the C flat so important?

If we look in the next measure, we will encounter our controversial chord again on beat four. It continues series of chords that looks like something out of Debussy: four dominant seventh chords moving chromatically in parallel motion.

But what appears to be "advanced" harmony is really only interesting voice-leading. We find hidden in these dominant seventh chords a series of quite ordinary parallel diminished seventh chords with the alto voice arriving one 8th-note late on beats 3, 4, 5 until beat 6 where Chopin is forced by the rhythm to bring it in within the beat, and we finally hear the actual diminished chord:
It is clear now that Chopin is preparing our ears for this audacious voice-leading trick by placing the C flat on either side of the B flat chord. To play a C natural here creates a chromatic conflict between the C natural and C flat that can be heard in the following example:
I think that music editing that does not make use of analysis loses a powerful tool.

For me Cb looks as the double diminished 7-chord, very common in the Baroque/Classic with inversions:
https://en.m.wikipedia.org/wiki/Augmented_sixth_chord

(If I see correctly from my tablet...)

I don't see clearly the manuscript, is that any sign of the natural on the last note in the cross staff? That should be than SOMETHING...

OCTO. while the altered chord is quite ordinary in itself and doesn't bother you or me, the editor of the first German edition and several generations of editors until the present have apparently found the two chromatic major thirds in a row problematic in this context (exposed on top of the chord). Chopin, who sometimes altered parallel progressions that few others have found objectionable, may also have been concerned about it and for this reason inserted the appoggiatura E flat to break it up. Chopin probably thought of the rising series of major thirds in measure 7 along the lines of my analysis above, as disguised minor thirds. Such disguised chromatic progressions are not uncommon in his music.

I do want to add that the analyses are from Schenkerian perspective, where simply giving a chord a name is not considered sufficient to account for its existence and every dissonant note in a chord (and that includes the sevenths in ALL seventh chords) must be explained in terms of voice leading.

The little diagonal line before the final C flat is probably a crease in the paper or maybe a slip of the pen. It looks nothing like a natural sign under high magnification and there would be no reason for a natural at this point in any case because Chopin would have placed it before the previous C.