I think 476 AD as an end date was a little conservative on CA's side, but I understand where they're coming from since the last western roman emperor was removed in 476 AD.

I think it should have been more along the lines of 600 AD or so as the end date, since during the dark ages there was probably only a couple empires that were established, the rest were either barbarians slowly progressing towards an early medieval culture or empires in chaos.