Each DVC ownership is represented by an ownership interest in a unit of the larger DVC resort. A unit might be 6 different rooms that they package together when they setup the points.
edit2: To provide more clarity, when DVC declares portions of the resort so they can sell points, they package up chunks of the resort into units. They don't declare the entire resort at once, I think BLT had 17 different amendments when it was being sold, releasing points grouped into units by phases. So Phase 18 of BLT has Unit 18A and 18B. Unit 18A is 2 x 2 bedroom rooms, while 18B is a single 2 bedroom room. So unit 18A will have twice as many points as unit 18B.
For instance my deed is for "An undivided 0.4575% interest in Unit 89B of Bay Lake Tower at Disney's Contemporary Resort" which is 160 points. ***
Now say they have someone who wants 300 BLT points and DVC owns 160 in Unit 89B already. They need another 140 points in the same unit to sell the 300 to that person, so if my contract came up for ROFR they might pay more to take it since they need points in the same unit to sell to the new 300 point direct buyer. They can't package up random points from different units and resell them as a larger contract.
I've said this before, and I'll say it again. The initial buy in cost of DVC points is a rounding error in the overall cost of DVC ownership. I wouldn't even bother trying to save 4 dollars a point on a contract. Buy the contract with the number of points and use year that works for you. If I found a good 50 point contract that met my needs I'd just offer full price. Trying to save 200 dollars on a 50 point contract, when using DVC costs as much as it does is almost pointless and not worth the hassle. I understand human nature is to try to get the best deal and feel like you've "won" a negotiation, but I just feel like with DVC it doesn't matter.
*** if anyone is interested, Unit 89B maps to either room 8534 or 8536 at BLT which is a grand villa. I'm not sure which one it is, but yeah my DVC interest is about 9 square feet of a grand villa if that puts things in perspective. You can look up document 20090412099 on the OCC website