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In the sources there is no 
before a1 (in the case of JC and PE it concerns bar 66, repeated here as bar 102). It is related to a different range of the octave sign at the beginning of the bar: the second semiquaver triplet is still embraced by it, which makes that the at the pitch of a1 (in the notation) appears already before the 6th semiquaver of the bar.
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category imprint: Source & stylistic information
issues: Accidentals in different octaves
notation: Pitch