All sources feature a 
to the G quaver. This accidental, in A written at the pitch of B, is a remaining element of the initial version, in which the 2nd half of the bar was the same as in the preceding bar. According to us, it could have been the initial version, changed in order to achieve a smoother transition – without repeating C – between the bars, or simply a mistake, consisting in copying the fragment of the preceding bar. In the main text we omit this unjustified accidental.
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category imprint: Editorial revisions; Corrections & alterations; Source & stylistic information
issues: Corrections in A, Errors resulting from corrections
notation: Pitch