I think you hit the nail on the haystack. There are only certain units deeded as fixed weeks. Once they sell all the fixed weeks, they're gone. They would have to ROFR another fixed week to sell you a fixed week, which is like finding a needle in said haystack. Regardless, it's going to be more difficult once VGF sells out and therefore your guide may be less willing to go to any heroic measures when they could be selling Poly deeded weeks. I'd plan for purchasing before they sell out. That said, they were on track to sell out in April, but the announcement of Poly sales probably slowed down sales as people hold off new purchases until Poly goes on sale. I'd guess VGF slows to a trickle and lasts through the end of the year--pure baseless speculation, but that's where I would put my money.
Granted, there is a limited number of Guaranteed Week deeds that can be sold at the Villas at Grand Floridian. But DVD is authorized to sell up to 35% of each of the seven accommodation types, such as Lake View Studio or Standard View One-Bedroom, for each week. Even with this 35% cap, DVD could sell 2,444 Guaranteed Week deeds. Through January 23, 2015, it has sold only 247, barely a tenth of what it is authorized to sell. Furthermore, none of the accommodation types have maxed out for any week.
Some people believe once DVD has sold points as part of a traditional flexible point deed or as part of a Guaranteed Week deed, then the points must retain that designation for the life of the resort. There is nothing in the Master Declaration that supports this belief. Once DVD reacquires a deed, it can then resell those points however it so desires. Keep in mind that the provision granting the Guaranteed Week privileges is tied to the deed, not to the points. When the deed is reacquired, the provision goes away.
When a new deed is sold, DVD can add the Guaranteed Week provision to the deed as long as it has not exceeded the 35% cap for that accommodation type for that particular week. The only other limitation is that DVD has to have a Residential Unit that has enough points in it to underwrite the deed. If someone wanted to buy a two-bedroom Lake View Guaranteed Week deed, it would cost 685 points. Currently, all but one (Unit 07A) of VGF's 36 Residential Units has enough available points to fund a 685-point deed.
An additional constraint on DVD is that it cannot sell more than 98% of a resort's total points to the public. When DVD initially designates a resort as being "sold out", it means it will no longer actively market that resort, not that it has reached the 98% limit on sales. When Bay Lake Tower was labeled "sold out" in July 2011, DVD still had about 455,000 it could see to the public. DVD could slap the "Sold Out" label on VGF tomorrow, but it doesn't mean it must stop selling points for that resort.
As long as it doesn't violate the 98% cap on total sales and the 35% cap on Guaranteed Week sales, there is nothing to prevent DVD from selling its available points to the public.