It may be the same area, but it appears that Hesperosaurus mjosi specimen comes from different level of the Morisson formation and appears to be older than the Stegosaurus specimens. Given the time difference it's unlikely that Hesperosaurus mjosi is the same species as Stegosaurus stenops, as you say. Some paleontologists sink Hesperosaurus into the genus Stegosaurus, but consider it different species than S. stenops - S. mjosi. Anyway, it seems that this is not the opinion held by most specialists, and the majority sees this specimen as separate genus. So, given the fact that I'm not an expert on stegosaurus, I'll go with the current consensus and present this animal as H. mjosi.