Hellrush does have rights to PeaceN. This leads me to believe that whoever used that name was just digging up old real small tag names to hide under for some reason.
While this might be true in the later part. Who made up the decision that someone has ownership of a clan name?
Technically, in this game, the only thing that solidifies ownership, is by backing it up with force. So regardless of who owned it, whoever can hold it has the right to it.