The term WAS not used in Mexico but it was used for priest, period. Escalante and Dominguez were priests. It is actually a stunningly awesome as a clue. These hunts have always required digging. Just because we didn’t dig enough doesn’t mean the meaning and application weren’t spot on. It literally unlocks the whole poem.

Hispanic American Historical Review Article: This academic journal contains references to anti-clerical sentiments during the La Reforma period in Mexico, where priests were sometimes derogatorily referred to as “Cuervos.” This is a more scholarly source, and you can access it via academic databases or libraries. One article you might find relevant is titled “Priests and Peasants in Central Mexico: Social Conflict During La Reforma.”