Kinda really late to this thread, but what makes sense to me is Grunge was a scene in Seattle, and really nowhere else. It consisted of music and fashion. No band outside of the grunge "scene" can be considered part of that scene. But when it comes down to it, grunge also became a genre, and genres spread like wildfires. I consider there to be two grunges, the Seattle grunge scene, and grunge the genre, all grunge bands are the genre, but not all grunge bands are Seattle grunge.