The Hypothesis of a Calendar Reform of 1350 AD -1351 AD
Tena cites an array of sources (Leon y Gama; Codice Aubin; Chimalpahin; Codice Boturini) conveying that the New Fire Ceremony was observed on Ce Tochtli (1 Rabbit) at least until 1351 AD. He asserts that in this year the New Fire Ceremony began to be celebrated on the date Ome Acatl (2 Reed) in Tenochtitlan (Tena 1987: 98, Cuadro 1). Hence, the Aztecs moved the year of celebration from the year Ce Tochtli (1 Rabbit) (1350 ad) to the year Ome Acatl (2 Reed) (1351 ad). Moreover, Ome Acatl (2 Reed) became the day of the New Fire Ceremony. This happened only twenty-five years after the foundation of Tenochtitlan when the Aztecs were still suppressed by neighbouring cities and tribes in Central Mexico. Tena argues that this calendar reform was due to military defeats of the Aztecs one or two hundreds years before. It was the reform of history writing, after the order by tlatoani
Itzcoatl (1427 AD - 1440 ad), which projected Ome Acatl (2 Reed) back in the official Tenochtitlan annals, recorded in pictorial documents and on stone monuments, as the single date of the New Fire Ceremony. This constructed historiography is why the extant sources operate with Ome Acatl (2 Reed) as the only date of celebrating the New Fire Ceremony throughout Aztec history (Tena 1987: 92-93).