I am convinced it is not a form of Agave parryi, as you say those really do not come with any strong mammillate margin features at all. I threw out kichijokan since it looks like it a lot more than it looks like Agave parryi, but even for those plants it would appear to be a little too mammillate.
Actually if I look at some of the pictures here:
http://www.agaveville.org/view...
Some appear to have pretty mammillate margins...
