Here is the essence:
Any player who plays in a qualifying tournament - no matter what age group - is locked on that team's roster for any and all qualifying tournaments. So if a 12U plays up to 16U, they are locked on that team's roster for the balance of the year - UNTIL NATIONAL CHAMPIONSHIP TOURNAMENTS. (So anyone who plays in a qualifier is locked to that team for all qualifiers.)
Once qualifiers are over, a team may pick up no more than three players WHOSE TEAMS ARE NO LONGER PLAYING IN ANY QUALIFYING TOURNEY and add them to their championship roster.
No player may appear on more than one championship roster, even if they are different age groups.