My answer to that would be a very firm 'So what'. If a player is associated with your band in some way and is happy to perform for them then that's simply the way it is. The only criticism I can see of fielding the players you want, whenever you want, is that some bands may simply replace their existing players with better players come contest time. This can have one or more of several effects.. 1) It could help to encourage the existing players to improve 2) it could mix things up so that players experience different levels of playing, and different outlooks to playing 3) it could put players off, ancd cause problems for the band long term and plenty of others.. Regardless of the outcome, this is a thing for the band themselves (and/or each contest) to deal with and suffer the consequences (or benefits), and should have nothing to do with some centralised registration facility to police.