I agree it can be difficult, both make woolly white spined plants. Some forms can be more easily separated but with some, I must admit to being stumped.
According to the descriptions, albilanata oaxacana is to 12cm tall, 13 to 27 radial spines, 1-6 central spines 4 to 7mm long, tipped brown. supertexta is similarly tall, 16-18 radial spines, and 0 to 2 central spines, short, 3-5mm only and tipped yellow to black.
Clearly they overlap in pure numeric terms, and while the supertexta forms which have no central spines, or only 2 very short ones, are relatively easy to separate from the rest, some forms are just similar to albilanata. The ssp. oaxacana includes quite a number of obsoleted species names, and some of these have a distinct appearance, but the botanists say they are the same.
I sometimes wonder what a DNA analysis would say about these? Their distribution areas overlap to some degree. Is there really a difference? Or is it that because supertexta is the older name that they have been left un-lumped?