20 Pesos Pattern, Calendario Azteca, Uniface

Pattern coinage from the Mexican Revolution period occupies a strange bureaucratic limbo — the country had been tearing itself apart since 1910, with Carranza, Villa, Zapata, and Obregón each issuing their own emergency currency. By 1917, Carranza's Constitutionalist government was attempting to reassert monetary legitimacy following the promulgation of the new constitution in February of that year. Lead was used for pattern strikes precisely because it was cheap and the dies could be tested without committing silver or gold to pieces that might never reach production.

PL#140 designates this in the Pollock reference for Mexican patterns. Uniface production confirms this never progressed beyond early die trials.