I just recently learned that this policy changed a couple years ago.
For the longest time the 11-month and 7-month windows were calculated from the *checkout* date, but then Disney changed it to be the *checkin* date as mentioned by the previous poster.
My guess is that DVC got tired of Members calling in every day to add one day onto the end of their reservations until they'd booked their entire trip.
We are wait listed right now for our VGF stay in December...our 7 month window is on the 29th so I will definitely be checking my options as a back up.