The Hypothesis of a Calendar Reform of 1506 AD -1507 AD
Emily Umberger argues that a famine was caused by a flood in 1499 AD. This lead to the calendar reform of 1506 AD - 1507 AD by Motecuzoma [II]
(Umberger 1981a: 191-192). Folio 41V (fig. 14)—Folio 42R (fig. 11) of Codex Telleriano-Remensis87 accounts that in the year Ce Tochtli (1 Rabbit) (1506 ad) the date of the New Fire Ceremony was changed from Ce Tochtli (1 Rabbit) (1506 ad) to Ome Acatl (2 Reed) (1507 ad), due to calamities that had occurred in Ce Tochtli or 1506 AD (Quinones Keber 1995: Folio 41V- Folio 42R, 86-87; 228-230; 274):
Year of thirteen houses (13 House) and 1505 there was a great famine in the province of Mexico; to get bread they went to the province of Pauco. Year of one rabbit (1 Rabbit) and 1506 there were so many rats in the province of Mexico that they ate all the seeds; and so they went out at night with lights to protect what was sown. In this year Motecuzoma killed a man in this manner; the ancient ones say it was to placate the gods since for two hundred years there had been hunger in the year one rabbit. In this year they were to bind the years according to their count, and because it was always a difficult year for them, Motecuzoma changed it to two reeds (2 Reed) (Quinones Keber 1995: Folio 41V, 86; 274).
The folio preceding folio 41 is missing. The second section of folio 41V relates, as folio 32r, of calamities—like starving and death—occurring 52-years before. This befell in the years Matlactli Omeyi Calli (13 House) and Ce Tochtli (1 Rabbit) under the reign of Montecuhzoma Ilhuicamina [I]. “Hand 5”, who wrote the historical notices at the end of section 41v, notes that the old Aztecs said that Motecuzoma [II] had sacrificed a man in order to conciliate the deities because there had been famines in the year Ce Tochtli (1 Rabbit) for two hundred years. But Historia de los Mexi- canos por sus Pinturas and Barlow connect this ritual arrow sacrifice to the conquest of Tzotzollan, which is later related in Codex Telleriano-Remensis (fol. 42r.). “Hand 6” claims, because of the famine, the years could no longer be bound in Ce Tochtli (1 Rabbit) or 1506. Motecuzoma [II] therefore changed the New Fire Ceremony to the next year, Ome Acatl (2 Reed) or 1507 (Quinones Keber 1995: 228-230).
Codex Telleriano-Remensis presents however, conflicting information of the calendar reform of the New Fire Ceremony. We have seen that folio 27v of Codex Telleriano-Remensis may exhibit a calendar reform of 1246 AD - 1247 AD, whereas folio 32v, of the same codex, indicates a calendar reform of 1454 AD - 1455 AD. 
The extant copy of Codex Telleriano-Remensis embodies 50 folios (100 pages) but several have been lost. This pictorial document was compiled from a range of sources after the Spanish invasion. Codex Telleriano-Remensis is thus not of a Pre-European origin. The manuscript is a hybrid document painted by numerous native artists and commented upon by both Spanish friars and Nahuas. The images were probably painted c. 1554 AD - 1555 ad, and the last annotation was appended in 1563 AD Codex Telleriano-Remensis encompasses three pictorial sections. The first section embodies the rituals of the 365-day calendar with historical annotations. The second section incorporates the ritual 260-day calendar (tonalpohualli) of the tonalamatl and is also associated with the nine day cycle of the Lords of the Night. The third section contains historical pictorial annals (or year counts), in three parts, which begin in the year 1198 AD and terminate in 1562 AD. The historical section was based on a native historical document. The first part of the historical section is a migration account, the second is a dynastic history of the Triple Alliance including a variety of astronomical and meteorological events, and the third relates a colonial history of the events in Tenochtitlan-Mexico City after the conquest but from the perspective of the Nahua. Codex Telleriano-Remensis, then, was collected unsystematically—it probably contains local histories—and must consequently be read critically owing to the conflicting information and because its sources are generally obscure (Quinones Keber 1995).
Nevertheless, other data corroborates the information given in folio 41v-42r of Codex Telleriano-Remensis, regarding the initiation of a calendar reform in the years 1506 AD - 1507 AD. The difficult years, with flood and cease of rains, between 1499 AD - 1506 AD can have motivated a calendar reform in 1506 AD - 1507 AD. Umberger claims that various monuments of Motecuzoma Ilhuicamina [I] and Motecuzoma Xocoyotl [II] indicates a calendar change taking place in the year 1506 AD (Umberger 1981a: 220-221). Ce Tochtli (1 Rabbit) is the date of (the archaeological) Phase IV of the Templo Mayor of Tenochtitlan. Duran maintains that his date was inscribed next to the portrait of Motecuzoma Ilhuicamina (I) at Chapultepec. The portrait of Motecuzoma Xocoyotl [II] is, conversely, inscribed with the date Ome Acatl (2 Reed) (Umberger 1987: 443). Umberger concludes that:
... 2 Reed is not an inscription found at the Templo Mayor, where most of
the remains are from before Motecuzoma II’s time. In addition, important sculptures that I believe date from the period between the two Motecuzomas (e.g., the great Coatlicue) feature the date 1 Rabbit alone; and the monuments that feature 1 Rabbit and 2 Reed together (e.g., the Temple of Sacred Warfare (Caso 1927), or just 2 Reed with a rope to signify the binding of years (e.g., the Chapultepec portrait) seem to be in the latest Mexica sculptural style and are generally dated to Motecuzoma II’s time... . (Umberger 1987: 444).
This suggests that a calendar reform of 1506 AD - 1507 AD came about during the reign of Motecuzoma Xocoyotl [II] ( r. from 1502 AD - 1520 ad), and not under the rule of Motecuzoma Ilhuicamina [I] (tlatoani until 1468 ad), since Ce Tochtli (1 Rabbit) was still the date of the New Fire Ceremony under the last mentioned tlatoani’s reign.
Three serpent heads were detected at the corner of the streets Cuba and Palma in Mexico City in 1944. A sign for a bar and three dots is carved below an Ome Acatl (2 Reed) date on one of these serpent heads. Given that the serpent head does not appear to be carved in an Aztec style  , Caso has championed the idea that this sign symbolised eight 52-year calendar cycles (from 1507 AD backwards) since the first New Fire Ceremony was celebrated, after the Aztec’s departure from Aztlan, in 1116 AD (Caso 1967: 15).9° Umberger advocates that these heads were commissioned by Motecuzoma Xocoyotl [II] in 1507 AD with the purpose of legitimising the calendar change of the year of the New Fire Ceremony from Ce Tochtli (1 Rabbit) to Ome Acatl (2 Reed) (Umberger 1981a: 94-95; 238-239). Moreover, she maintains that the dates Ce Tochtli (1 Rabbit) and Ome Acatl (2 Reed) were carved together on three monuments—the Xochicalco-Style Xiuhcoatls, the Teocalli (fig. 15), possibly the fragmented Escalerillas relief and on the Acacingo cliff relief (fig. 16)91—in order to justify the calendar reform of 1506 AD - 1507 AD (Umberger 1981a: 133; 218-220; 238; 270-271). A similar legitimisation for a calendar reform can be found in Codex Aubin
and Tira de la Peregrinacion, which operated with eight New Fire ceremonies celebrated on Ome Acatl (2 Reed) (Saenz 1967: 16). Presumably, Mo- tecuzoma [II] can have decreed a systematic rewriting of Aztec official history because nearly all the written and pictorial documents announce that Ome Acatl (2 Reed) was the date of the New Fire Ceremony since the Aztec left Aztlan (Umberger 1987: 444). 
-  Codex Telleriano-Remensis, named after its previous owner the French Archbishopof Reims, Charles-Maurice le T ellier is located in the Bibliotheque Nationale of France (Ms.Mex. 385).
-  Manuscripts organised as annals were called xiuhamatl or xiuhtlapohualamoxtli inNahuatl.
-  Nicholson maintains, however, that these artefacts are in a late Aztec style, whichreveals a Xochicalco influence (Nicholson 1971b: 112; 120-122).
-  9° Francisco de San Anton Munon Chimalpahin Cuauhtlehuanitzin asserts, in CodexChimalpahin, that the first Aztec New Fire Ceremony was conducted in 1091 ad (1997: 186187) but according to Gabriel de Ayala’s Year count the Aztecs had in 1247 ad bound theiryears four times in 1247 ad (Chimalpahin 1997: 221-222). This means that the first Aztec NewFire Ceremony had have taken place in 1039 ad.
-  A seated unidentified figure is shown on the Acacingo Rock carving on a hill nearMalinalco in the Toluca region (Mexico). To the right of his head are the dates Ce Tochtli(1 Rabbit) and Ome Acatl (2 Reed). Umberger comments that these dates are not carvedwithin a cartouche and therefore seem to be calendar names. They may represent thebeginning years of the 52-year calendar cycle (Umberger 1981a: 164-167).
-  In this connection Umberger comments that: “... Codex Telleriano-Remensis, thesource that records the change of the Binding of the Years to 2 Reed as occurring in 1507,also puts the previous ceremony in a 2 Reed year. Apparently the reform could be noted asa historical event, but was also necessary to project into the past. In Mexica history it wasimportant that the present and past be aligned and that like events should happen in yearsof the same name ...” (Umberger 1987: 444).
-  The day and year of the New Fire Ceremony mirrors an adjustment on the emphasisof the date when the earth was created Ce Tochtli (1 Rabbit) to the creation of the sun andmoon on Ome Acatl (2 Reed). The calendar reform may thus have signified that the Aztec,at the beginning of the 16th century, was now more interested in the creation of time of thecalendars (computed by the movements of the sun and the moon) than the primordialmaking of space (earth) of their cosmogony.