One thing that springs to mind about his point though - is it possible that "Maeshowe" was an older name for the site, that continued in use among the population throughout the Norse period, with the Norse name "Orknahaugr" being almost an official name that was used pretty much exclusively in writing? The same way you'll see "Spey Valley" written, but everybody still actually calls it "Strahspey" (not a great example, as "Strathspey" means "Spey Valley" - but the point is that the place has two distinct names, one you'll pretty much only see written, and one you'll pretty much only hear people say).