If you own points at more than one resort, and they are under the same membership--same UY and titled the same way--then you will be able to use the points at their own resorts at the 11 month window but at 7 months, will be able to easily combine them.
So, if you own BLT and then buy BWV, you would be able to use BLT points at 11 months at BLT, BWV points at BWV at 11 months but at 7 months, combine the books to book anywhere.
If you buy points at different resort and its a different UY or titled differently, it would then become its own membership and you would not be able to combine the points for a single night stay without a transfer.
Two UY's make things a bit ore complicated. If you add on via Disney, you will automatically get the same UY.
We have BLT and BWV but do have different UY's so two memberships. It is working out okay right now because we have 180 at one resort and 150 at the other so we can treat them as completely different.
Good luck!