Note that you can borrow and/or bank your BWV points even if you don't do the same with your VB points.
So if you bank one year and borrow another, you could potentially book 150 points at BWV at 11 months.
I think you could swap those out with VB points at 7 months BUT the banked and borrowed points stay in the use year of the reservation and cannot be banked, borrowed nor transferred.
Not sure why you'd want to do that unless say you wanted to book 150 points at BW early in your UY and then another 150 later. Like this for example:
UY Feb
In March, book 150 point stay at BW in Feb (with banked and borrowed points)
In July, swap VB points (this can be tricky if it is a busy time - your cancellation could potentially be grabbed by someone else I think)
In July, book another 150 stay at BW for June.