We add a cautionary flat next to b
2. The sign was added by someone else in A and printed in GE.
It is the first out of several signs added in A by GE's engraver or reviser. The additions are of random character – they were introduced only in the 1st, 5th and 6th page of the notation. A part of additions (e.g. the flat in the described bar) are cautionary signs justified with the musical narration, however some of them are either unnecessary (e.g. in bar 104) or grossly erroneous (bars 103 and 106).
Compare the passage in the sources»
category imprint: Differences between sources; Editorial revisions; Corrections & alterations
issues: Foreign hand additions in manuscripts, Cautionary accidentals
notation: Pitch