This is a very grey area indeed! Many great metal bands are borderline prog. But is it enough to merit inclusion? There are tons of Black, Doom, Power, and Death metal artist who I feel are more progressive than Queensryche or Fates Warning, but will never be considered for the archives. But I take solace in the fact that PA does focus on most of the unadulterated prog acts of the golden age. I've been exposed to many great albums, through this site; that I might not have stumbled across if it were more diluted with every release that bears the slightest semblance to prog.