If you are a prominent member you may apply in this campaign even when it's full. Users could be rotated out based on performance (not based on how much you post, more about how you post).
Merit, trust, standing in bitcointalk are all factors that will be considered so if you have a low number of merit earned, no trust ratings and are relatively new you will likely to not be added to this campaign.
Maybe when there is need you can still revisit previous applications and see if there would be some considerations such that people who previously applied may not flood this thread reapplying.