Ok, so just to share my experience in case it helps somebody else. The letter I posted above is not the correct one to request the Constancia de datos Registrales. I emailed the Mexican embassy and they provided the proper letter in about two days.
I live in Chihuahua city and the PGR office here does not process the Constancia, but they did help me to get my fingerprints taken free of charge. The nearest place to get a Constancia for me is Cd. Juarez so I sent everything to my father who lives there along with a Carta Poder so that he could request it for me. In about 4 business days they called him and said it was ready.
I live in Chihuahua city and the PGR office here does not process the Constancia, but they did help me to get my fingerprints taken free of charge. The nearest place to get a Constancia for me is Cd. Juarez so I sent everything to my father who lives there along with a Carta Poder so that he could request it for me. In about 4 business days they called him and said it was ready.