The 25% member discount through MS depends on availability. We have four nights booked at VB in mid-June. The first night (a Friday), we are paying full rack rate. The following three nights, the 25% discount was available, and the reservations have been linked. The 25% discount is never guaranteed. We will check in mid-May for availability of the first night at the member discount and make a change in the reservation if it turns out to be available.
We book VB stays to follow BWV stays that have been booked at 11 months. We use a combination of points and cash at VB. Sometimes the member discount is available as early as the 7 month booking window (apparently low demand periods). This has been the case for our early January stay each of the last two years. In other cases, we book what is available at rack rate, and call later to see if a member discount has become available. We have never had a problem changing from a rack rate to the 25% member discount if it has opened up prior to our trips.
I also usually check into AP discounts and watch the Disney Visa and Birnbaum discounts as well, although some of these are for Garden View Inn Rooms. We much prefer the Ocean View Inn Rooms, so some of these other discounts don't really work for us.
Ralph