Pin code discounts are mailed, emailed, or can be attached to your name. These are sent out randomly with no rhyme or reason as to who gets them and who doesn't. To find out if a pin is attached to your name, you would need to call and ask about it. Other general public discounts that come out are released when Disney sees low occupancy levels at the resorts and needs to fill rooms for a particular time period. If you book a trip and a discount comes out that would apply to your dates, you can call and have it applied to your current reservation. One thing to keep in mind, though, is not all resorts/room types are always offered with a discount and sometimes some resorts are offered at a lower discount than others. If a certain resort is at or near capacity, Disney sees no need to offer a discount on that particular resort/room type. You might have to be flexible with your resort choice in order to take advantage of a discount as having a reservation already in place does not guarantee a discount can be applied. With that said, you can change resorts, dates, etc. after you book, pending availability of what you want to change.
If you are going next year regardless of whether or not a discount comes out, I would book now to make sure you get what you want, but if your trip is dependent on a discount, I would wait to see what (if anything) comes out for your travel dates as booking a room now in hopes of a discount is one less room Disney will need to fill later on. As for the best resort for fireworks, our favorite is the Poly as the beach is a great place to sit and watch them. The CR is also great, especially if you book a tower theme park room as you can sit on your balcony and have a great view from there.
Good luck and have fun planning

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