Per mousesavers.com:
Be aware that discounted rooms are limited in number and will not be available for all dates at all resorts. You may have to be flexible with your selections. If you can't get your first choice on the first try, call back periodically and check on availability. Frequently discounted rooms will open up as people change and cancel their reservations over time.
Rooms are already booked up heavily for the October-December period this year, due to several factors, including:
tourism is finally recovering after 9/11 - more people are travelling in general
Disney has expanded its Food & Wine Festival and the number of nights of the Mickey's Not So Scary Halloween Party, making Fall a more appealing time to travel
many people have already booked the "buy 5 nights, get 7 nights" package that was offered back in May and June for stays through November
Disney has already offered many private e-mail discount codes that allowed the recipients to book discounted rooms through December
With all of these factors in mind, I'm actually a little surprised that discount codes were offered to the general public at all, particularly for October.
In any case discount codes must be thought of as a "clearance sale" -- if you want the discount, you have to be willing to take what's left over! It's important to be flexible with both dates and hotels, and to be persistent in calling back periodically to see if anything has opened up.
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I found this to be so true. I called that first day the ap discounts came out and still couldn't get what I was looking for. WDW has certainly rebounded!