As disneynutz says, DVD could not offer Guaranteed Week deeds for a
DVC resort built prior to Aulani unless it made changes to the resort's master declaration.
Even though VGF is 'sold out', DVD sold a Guaranteed Week in July 2015 (see
this article). DVD is able to sell a Guaranteed Week as long as (1) all the required points are available in a single Residential unit; (2) the number of GW deeds for that week and accommodation type does not exceed the 35% cap; and (3) the specific days for that GW deed are "immediately available" for booking. Plus, there is a fourth condition: DVD cannot sell more than 98% of a resort's total points to the general public. Right now, VGF is very close to that limit.
The first condition is somewhat limiting but every one of VGF's 36 Residential Units currently has at least 670 points, which is enough to fund even a Guaranteed Week deed two-bedroom villa. The second condition has not been reached for any accommodation type for any week, so that isn't an issue for the moment.
The third condition might be the biggest impediment to someone wanting to buy a Guaranteed Week. If someone was buying a GW deed for a week that is many months in the future, then those dates are probably still available for booking. However, if someone wanted a GW deed for the near future, such as this December, seven consecutive days aren't available to fund the entire week. And if they aren't available, DVD won't sell the GW deed.