Thomas Braatz wrote (October 13, 2002):
The KB of the NBA I/15 (1968) mentions, among the many additional marks/notations and numbering systems used to catalog the score and the set(s) of parts, a single mysterious entry found on the inside of the original cover that enclosed the score and parts: "Carl u Christel." Although written with the same ink, the word "Carl" was definitely not written by the same person who wrote "Christel" because the c's, r's, and l's were all written differently. It has been conjectured that these names were written at the time when the division of the inheritance (including the all the scores and parts of the vocal works of J.S.Bach) took place, thus distributing these 'shares' [isn't this ironic?] between the three sons, Carl Philipp Emanuel, Wilhelm Friedemann, and Johann Christian, the latter being referred to as "Christel" ("Little Chris[tian]") in the immediate family. By comparing the handwriting of the name "Christel," with other evidence material that is still available, it can be stated with near certainty that this name was written by no one else but Anna Magdalena. But since the other handwriting is still a mystery (an executor perhaps?), why were these names written on the cover for this particular cantata and not for other cantatas? It appears that this cover was at the top of the pile of cantatas that comprised a yearly cycle, not based on the Lutheran liturgical year beginning with the 1st of Advent, but rather on the anniversary date of Bach's 'assumption' of his post as musical director in Leipzig. [See Konrad Küster above] Christoph Wolff, in his biography of "J.S.Bach, the Learned Musician" (2000) also refers to these names and uses as an example a similar designation for the cantatas of the 1st yearly cycle.