i don't know the physics of it, but i have seen the physics teacher at the high school where i teach take two thin polarizing lenses and turn them so the polarization goes east-west on one and north-south on the other, then rotate one of them. you could see the change, so i imagine from that experiment that two different polarized lenses could be made from two different combinations of layers so that they have different polarizing characteristics. so it makes sense that some lenses do the same thing, but one better than the other.