Do you have a code or a PIN?
There are public codes (generally 3 letters) and can be applied to your reservation through an affiliation (Annual passholder, Florida Resident, general public). These are released (or may not be released) throughout the year. For example, it seems as though there are no general code discounts for May and June due to increased bookings, but Disney could surprise at any time. Public codes and historical information are on mousesavers.com.
There are also private codes (also 3 letters) that are sent to select people generally through a postcard. These private codes are attached to your specific name or address. You MUST have the postcard with you when you check in or you will (probably) pay rack rate. The reservation usually states this.
A PIN is 10 numbers and is generally attached to your specific name, e-mail, or mailing address. Although the offer can be the same, they too are private, and like the postcard you are the only one (under the rules) who can use it.
I am lucky enough to have a PIN for my June trip that came via e-mail to me. DH deleted the e-mail after I made my reservations. The CRO said that I did not need the original e-mail for my check-in - the PIN was "attached to my name".
There is generally great excitement on these boards when PINS and postcards come out for new time frames - it means that public codes (hopefully) are on the way!
If your trip is next December (2006?) it is unlikey that your discount could be applied to that. It seems to be too far out. Never hurts to ask, though.