There are various arrival dates and departure dates so I think that because of this there are people moving in and moving out at any given time. However, I do think that there are probably seasons or waves in which there are more people moving in then out at certain times so if you arrive during a time where essentially no one is moving out and many people just finished moving in then yes I think you'll have a difficult time getting the complex you want since a higher percentage of rooms could be taken. Despite this I do think that there are people moving out often and they could come from any complex so unless you arrive right after a time that's arrival heavy whether or not you have free choice of where to live is all up to luck.
Do cast member discounts count towards online purchases? Can they be used at
DisneyStore.com?