Mammillaria pilensis was a long forgotten name until Reppenhagen resurrected it for a plant that he found near Puerto Caroza in Guanajuato, and placed it under hamilton-hoytea.
In Hunt's classification he has a Group in the Mammillaria series, the Pettersonii group, which includes only two species - pettersonii and gigantea. The best known species of pettersonnii is also know as apozolensis v saltensis, but this actually is quite an extreme form of pettersonii. These two species do tend to intergrade in forms, so it is no great surprise that the attribution of the M. pilensis plant has been at varying times to both of them.
I have several formsof gigantea and pettersonii, and from observation of these prefer to ally pilensis Rep 800 with gigantea, as much because of the flowers as the spination.
I think it is one of these borderline cases that makes clear delineation impossible.