M. diguettii was described in 1904, 50 years after M. senilis, and apparently differed in having dark straw coloured spines and a smaller flower. Your plant with this name doesn't match that description as far as I can see. There don't seem to be any known living collections, though it would be good to know if there are. It was reported to come from Jalisco, up in the mountains like M. senilis, but maybe a southern variant, so its not clear if it is just a local variant or sufficiently distinct to be a valid subspecies (variety).
M. senilis is a lovely plant, so a darker spined form would certainly be something to have.