I can add that I’d tried for an exception too with my BWV purchase. The contract had 2016 points banked to 2017 and I’d would very much like to be able to use those points.
My new contract is for another UY
MS wouldn’t/said no to transfer the points to my other contract and then reallocate points for an upcoming booking.
It took two calls to MS on the second one I spoke to a cast member which worked his magic. He took my upcoming booking from contract 1 and moved it to contract 2. It was more a cancel/rebook thing without the rooms going into free availability as MS was holding them. That used all banked 2016 points and then he unbanked 40ish 2017 points which was banked to 2018 to complete the reservation.
That freed up points on contract 1 which is now banked into 2018.
My point is that MS might not be able to do what you are asking but maybe they can do something else. Also it might take more than 1 call to MS to get the pixi dust.
Worst case scenario you could either rent the points or take an extra vacation.