These questions cannot be satisfactorily answered as long as we do not have documentary evidence.
Speculation is justified, however, as there are certain biographical clues.
The proposed date, ca. It is reasonable to infer that Bach brought with him a set of music including WTC II, though it was still incomplete. This locational information, Berlin, is also suggested by a number of other sources of the Group. Secondly, it is significant that in Hamburg the missing movements were later supplied from A1 by the scribe different to that responsible for the rest of the movements, and many movements were also corrected subsequently, possibly using the same correction exemplar. All of the other sources belonging to this Group contain all these revisions, except H2 in Pr.d.