I was checking my maps today, and these three plants (brachytrichion, pennispinosa and the new plant) all come from the north of the state of Durango.
M. brachytrichion is reported from General Escobedo, M. pennispinosa from between Mapimi and Bermijillo, and the new plant from Arroyo del Canallo in the commune of Coneto de Comonfort. I have checked the distances between these locations and the direct line distance between General Escobedo and Mapimi is about 135km, between General Escobedo and Arroyo del Caballo about 85km, and between Mapimi an Arroyo del Caballo about 115km. These locations form an inverted triangle with Arroyo del Caballo at the apex or further south.
I note that very close to Mapimi is Ojuelo, the location, I believe of Reppenhagens ojuelensis.
Having checked through some of my books, while a number of other Mamms come from Durango, in the north there seem to be only two - nazasensis and sinistrohamata. This last one is reported (along with many others) from Minas Navidad, the same location as the type location as nazasensis. This is less than 30km from Arroyo del Caballo.
I also have read that Luethy in his classification sinks brachytrichion, pennispinosa and nazasensis beneath sinistrohamata.
I think that this just says they are all closely related - for me it is a distinct form and well worth cultivating - no matter what name it ends up with.