I would ask for two figures separately and in writing: the amount that applies before possession and the rule that applies afterward. I would also ask how each one is adjusted and from which date.
I would not treat figures posted in forums as current. They are useful for discovering the right questions, but the current contract and a written projection should be the main references.
I would also ask which event triggers the move from one stage to the next: allocation, physical delivery, title deed or another condition. Understanding that date helps a lot with budgeting.