facts · conversion withheld
Exact arithmetic does not create an exact epoch
Once a reference day is chosen, modular arithmetic can generate an answer forever. The unresolved question is whether that reference and its treatment of the seasonal year reproduce a particular historical count.
Three controls block a generic calculator
colonial record
The witnesses conflict
Bartl, Göbel and Prem found contradictory European alignments and disagreement over whether the annual sequence began with Atlcahualo or Tlacaxipehualiztli.
seasonal year
A bare 365-day projection may drift
Ezcurra, Ezcurra and Meissner argue that horizon observations and Mount Tlaloc alignments could maintain agricultural timing against the solar year.
modern reconstruction
A result belongs to a model
Recent scholarship can generate precise Gregorian correspondences, but only through explicit choices such as a Caso–Nicholson alignment. Precision is not consensus.
Future converter contract
A future tool must name its correlation, identify the source family and regional scope, state its year-start and adjustment assumptions, publish independent historical fixtures, and show rival outputs when one date can honestly resolve more than one way. Until then, no birthday receives an “Aztec sign” here.