five-month period of mourning following the February 1st death of Elector Augustus II and before July 27, when Bach presented the successor, Augustus III of Poland, with the Missa as a set of instrumental and vocal parts. It is possible that the Kyrie was meant as mourning music for Augustus II, and the Gloria as celebratory of the accession of Augustus III. In the mid-1740s (c. 1743–46). Bach re-used two movements from the Gloria in a cantata for Christmas Day (Gloria in excelsis Deo, BWV 191). Gregory Butler argues that at the same service (which he dates to Christmas 1745, to celebrate the Peace of Dresden), Bach also used the 1724 Sanctus, and that this revisiting of the 1733 Missa suggested further development to the composer. In the "last three years or so" of his life, Bach wrote/assembled the Symbolum Nicenum and the remainder of the work; many scholars, including Christoph Wolff, believe he did so in 1748–49. This dating in part reflects the scholarship of Yoshitake Kobayashi, who dates the Symbolum Nicenum section to August–October 1748 based on Bach's increasingly stiff and labored handwriting. Wolff among others argues that the "Et incarnatus est" movement was Bach's last significant composition. The words had been included in the preceding duet, but then Bach decided to treat them as a separate movement for the choir, giving the words extra weight and improving the symmetry of the Credo. John Butt argues that a definite final date of August 25, 1749, can be given, in that on this date C. P. E. Bach completed a setting of the Magnificat with an "Amen" chorus that "shows distinct similarities" to the 'Gratias' from the Missa and the 'Et expecto' from the Symbolum Nicenum." C. P. E. Bach later reported that he performed this Magnificat (Wq 215) in 1749 in Leipzig "at a Marian festival ... during the lifetime of his now-deceased father". Title Bach did not give the B minor Mass a title. Instead, he organized the 1748–49 manuscript into four folders, each with a different title. That containing the Kyrie and Gloria he called "1. Missa"; that containing the Credo he titled "2. Symbolum Nicenum"; the third folder, containing the Sanctus, he called "3. Sanctus"; and the remainder, in a fourth folder he titled "4. Osanna | Benedictus | Agnus Dei et | Dona nobis pacem". John Butt writes, "The format seems purposely designed so