Alright, just as an example, let's take All the Young Dudes. It was written by David Bowie for Mott the Hoople to perform. Mott the Hoople had a big hit of it. Mott the Hoople were the first people to record it because Bowie gave them the song.
David Bowie then recorded his own version of the song later.
Supposing Bowie or Hoople wanted to put All the Young Dudes on the Rock Band Network, which one would count as the "cover" and not be allowed?