Sold out only means not currently being marketed or actively selling. Disney does acquire points at resorts through the ROFR process and at any time, has points available at 'sold out' resorts. If they don't currently have points available, you can be added to the waitlist. They also don't offer much, if any, incentives to those resort points.
You might check out the resale market where you can save a lot of money. You can also become a member with less points via resale. Then you can add on any number of points direct. Going direct right out of the shoot requires a minimum 150 pt. purchase. Just be aware of any restrictions that may come with that purchase. We have both resale and direct points. It also takes a few months to go thru the process while direct is quicker. We had out paperwork within and hour and points within 5 hours for our last add on. Resale process takes approximately 2-3 months.