You can make the June 2017 VGC reservation, assuming availability, at 7 months out in Nov. At the time you make that reservation, you will be able to use for that trip any points banked from your Dec 2015 use year, any points from your Dec 2016 use year, any points needed via purchasing up to 24 one time use points, and, if needed, borrow points from your Dec 2017 use year.
Be aware, however, that VGC could be difficult to get at 7 months out because it may already be full, so you may need a back-up plan. Also be aware that if you need to purchase one-time use points to reserve VGC, you will have to call to make the reservation at 9 a.m. when MS phone lines open rather than at 8 a.m. eastern, when one can reserve online at exactly 7 months out, because that purchase of one-time use points can only be done via phone. Moreover, be aware that if VGC is actually open at 7 months out, your odds of getting it will likely exist if, and only if, you make the reservation online at 8 a.m. eastern because when VGC is open at 7 months out, it often books full in less than a minute after 8 a.m.
Finally, if you are inteding to get Aulani for June, you should make that reservation exactly 11 months out from date of arrival to be safe because June is Aulani's highest demand time of the year