I do have to qualify my post above in that I am drawing upon the use of saltpetre from Chile and that bat guano was used in US gun powder production.
My post was about the possibility that sodium nitrate was used in Mexican gun powder production. The reports are consistent with that but the source of Mexican saltpetre is unknown to me as is it's chemical composition.
gives a brief overview of saltpetre over history for gun powder. Chilean saltpetre was
actually used for gun powder but not good powder and was being converted to normal saltpetre in some quantity late in the 19th century industrially but black powder firearms powder demand dropped drastically with new nitro smokeless powder but remains important for the ignition of artillery shells today. The sporting use is only a small fraction of the military demand these days.
From the Mexican perspective it was the cheapest source of a saltpetre, direct from Chile by ship, compared with buying ready made gun powder from the USA or Europe. I can see it being a possible commercial choice for the core firework and blasting powder production in Mexico. Again I know little of what they actually did in Mexico other than that they did make gun powders in some form or forms.