De Smeth & Fayolle, Les Premieres Emissions du Mexique (1856 a 1874) , p. 208, noted that “There are also a certain number of varieties, resulting from the relative imperfectness of the printing process”. They only mentioned one variety for the 7 centavos in which “The figure to the right is a 1.” Page 26 of the accompanying catalog stated: “Price of the ordinary to be doubled.” That seems too conservative if there is only one flaw per sheet, but maybe they considered demand.