Just for further clarification, you may sell add-on points separately, whether they are at the same resort or a different resort. Add-ons of less than 150 points through Disney must be the same use year. If you have a single use year, even at different resorts, Disney will keep them all in the same membership, which is nice when it comes time to bank because the % allowances are based on the total points in the membership number.
We have a single membership and use year and 6 contracts, 5 of which are at BWV. When making ressies I only worry about whether I am using BWV points or OKW points. The multiple add-ons at BWV act like one contract when making ressies. (But I have the advantage of being able to sell those add-ons separately, heaven forbid.) I think the only time it might be necessary to distinguish points on my BWV add-ons would be if I were going to sell an add-on because I would need to decide where the banked/current/borrowed points would go.