Hopefully you'll get a definitive answer from a member who is a comp organizer. However, I assume you are referring to Pro-Am events which are less strictly regulated. Indeed, I have also observed that there are couples that compete at the bronze level "for ever." Newcomer events reflect only competition experience and not skill level.

Amateur competition rules allow us to enter only two adjacent levels so we do not see gold level competitors in bronze events. I have been allowed to compete at multiple age levels providing they are at or below the oldest level for which my partner and I are eligible.