You may buy up to 24 points, at $19 pp, at the 7 month window. By phone. The unit MUST be available at 7 months to use them, and you can't swap them in for home resort priority points if the unit is not available to the general public.
You cannot book a stay that is 210 points when you have only 200. If it is home resort, you will have to borrow, or roll the dice that you will be able to book your last day at 8AM+phone hold time of 7 months.