I'm going to answer to myself, since above is already a tl;dr and it's unlikely that these comments will attract any kind of attention. Note to self. There's a

I'm going to answer to myself, since above is already a tl;dr and it's unlikely that these comments will attract any kind of attention. Note to self. There's a subtler political point that the paper is trying to make, neither vaquero tradition, nor historic accounts by colonists can strongly testify to the existence of indigenous sacred tradition in the 1600s. This are my suppositions, but I suspect what when the various conquistadors were exploring North America, they wouldn't be privy to the burgeoning sacred equestrian tradition of the indigenous tribes. By the time anglos cross the continent and establish strong enough ties to learn of such a sacred tradition, it becomes impossible to date exactly the tradition's beginning. The paper tries very hard (with talk of care, and quotes from tribe representatives) to establish that such a tradition was already establish in the 1600s, so by the time there was a contact with anglos, indigenous peoples really really knew what they were doing.