In your example, if Disney bought back a 200-pt contract, they could break that contract up and sell it in smaller increments. For example, those points could end up being sold as a 50-pt, two 25-pt, and one 100-pt contract, all with the same resort, UY and Unit number as the original.
If Disney buys back more than one contract from the same Unit number within a resort, they could combine those into a larger contract. I sometimes wonder if the seeming randomness of ROFR is due to Disney snapping up a contract from a particular Unit so that they can combine it with another (small, leftover) contract from the same Unit to make a larger one to resell.
For example, imagine Disney has 10 or 20 points left over from breaking up a larger contract. While it has happened that someone was sold an add-on that consisted of two contracts (one for 10 points, the other for N-10 points) I imagine Disney would prefer not to do that. So if they see another contract for the same resort and Unit number during their ROFR review, they might be more inclined to take that one so that they can combine it with the 10 points they had left over to create a larger contract that can then be broken up into pieces of 25-points and larger. As far as I know, they can only do this with contracts that are from the same Unit number within the resort.
Of course now that Disney rents points to members at $15 a pop, those little leftover contracts are nice little money makers for them so this may be less of a concern than it was in the past.