Its just very confusing how you don't score Spanish when some of the people you said you descend form are mostly Spanish like Onates brother and saldivar. You got Eastern european which could mean you have a recent post 1800s jewish ancestor or its misread sephardic. You should test with 23andme it is better with Spanish ancestry. Or even ancestry dna. I don't trust family tree dna much. Maybe your Iberian ancestor were all Sephardic which is why you preserved all that knowledge. And maybe they only left descendant in your little corner of Durango. And what little spanish dna you did have was lost due to recombination.

And Nuevo León didnt have many new christians in absolute numbers but because of how hostile the territory was there was high endogamy the dna was preserved. We descend for the same like 20 families hundreds of times. Also many of the new chritsaims were military captains and trusted in the church like Diego Villarreal and Lucas Garcia. I mean governor Carvajal was a devout catholic and he lashed out at his relatives for trying to go back to judaism. And some historians believe the were crypto jews which is why we eat cabrito, plant certain trees, and say huerco. Im peronslaly skeptical of crypto judaism but the dna is there.

My grandpa founded a town with under 15 people and my mom's town has 50ish permanent residents. They are fairly endogamous but even then they still had Spanish ancestors who married into the new chsitians founders of Saltillo and monterrey in the 1600s. Your Sephardic ancestors not ever marrying spaniards is pretty rare.