So when deciding availability for BLT are they assuming that all rooms will be built and ready or do more rooms become available as they get completed? I hope this question makes sense.
this is true. All of BLT is being built, but you can't make reservations for a unit until it is declared into inventory. DVC will declare a unit in to inventory, and all the points that it represents can now be sold. Once those points are sold, they will declare another unit in to inventory.
The undeclared units are sold for cash reservations through CRO and the money generated by those reservations goes to DVC.