It's been claimed that the H/P stone was created by an old Mexican friend of the family, with a young girl's coloring book having been the source of the image used for the horse on the stone. I have spoken on the telephone with the lady who told me she owned that very same coloring book as a child. If true, it kinda blows apart the theories of the artist not having Spanish as a first language IMO. Others, who were part of the same research group have related the same story to me and a few other listeners as well . It also unfortunately, would negate your "coincidences" for all practical purposes .