Supposedly a Player earns his Number once he earns/wins his Roster Spot--not including high draft selections who are slotted in from Day One... or are deemed Number-Worthy--So, when the Players are deemed 'ready', they will get their Regular Number, and cast aside their Rookie Number for good... That of course is not to say that a Player cannot gain his Regular Number and not be demoted and promoted afterwards as the GM sees fit; IIRC Laughton is a good example of such a situation.