Luther on Christmas Day as the first day of the properly Christian New Year

"Today is called New Year's Day according to the computation of the Romans, but for us Christians, [the first day of the new year] is [the day of] Christ's Nativity."

"Es heist hodie des new jarstag secundum computationem Rhomanorum, sed apud nos Christianos est Christi nativitas dies."

     Martin Luther, Sermon on New Year's Day (1 January 1528), WA 27, p. 1, ll. 2-3.  Cf. Morning ("früh") Sermon on the Day of Circumcision (1 January 1531), WA 34.1, p. 1, ll. 3-11 (there follows the sermon preached in the afternoon ("nachmittags").

     The conclusion must therefore be the following:  "Luther could indeed render his tribute to the beginning of the year secundum computationem Rhomanorum, but he treated Christmas Day as [the] real beginning of the New Year on theological grounds, and adhered to this, in the dating of his letters, his whole life long.  For the conversion of the date and its testimony [(Angabe)] into [our] modern [style of reckoning], what is required is not a special rationale [(Begrundung) for] the acceptance of the 'old' beginning of the year on Christmas Day, but an inadvertent [(etwaige; but Schneider has just, on p. 115, appealed to slips of the pen or "Feder")] deviation from the [Lutheran default, i.e. the] Christmas Day style" of reckoning in a mere 8 out of the 34 relevant cases (Hans Schneider, "Weihnachten als Jahresbeginn und der Weihnachtsstil bei Luther," Lutherjahrbuch 84 (2017):  115-116 (82-117), italics mine).  Cf., as Schneider points out on p. 86, the last stanza of his Vom Himmel hoch (1534-1535), as translated by Catherine Winkworth in Lyra Germanica (1855):

Lob, Ehr sey Gott jm höchsten thron, | Der uns schenckt seinen einigen son. | Des freuen sich der Engel schar | und singen uns solch neues jar.

Glory to God in highest heaven, | Who unto man His Son hath given! | While angels sing with pious mirth | A glad New Year to all the earth.

     As for "the 'old' [(or pre-Luther-an)] beginning of the year on Christmas Day," see Schneider, p. 81, as well as pp. 116-117 (Johannes Agricola, Melanchthon, and Spalatin; Duke Georg of Saxony, Count Philipp, Elector Johann Friedrich, the City of Constance, and other princely and municipal chanceries).  Cf. also A. N. S. Lane, "When did Albert Pighius die?," Nederlands Archief voor Kerkgeschiedenis 80, no. 3 (2000): 330, 338 (327–42):  "in Utrecht the New Year was then normally reckoned to begin on 25 December.  It was not until 1575 that this was changed to 1 January".

     Of course, even "the beginning of the year secundum computationem Rhomanorum" Luther refused to treat as anything other than the Christian Feast of the Circumcision.