The current room discount bounceback for dates in 2018 is in effect til August 15. If you are staying at Disney in early August, that is what will be available to you. Disney has offered free dining for the following year after that, but who knows what they will do this year. Resorts are booking even at rack rate. Also, make sure you check the dates covered by last year's offer. December dates are usually pretty limited.
*just saw you want free dining bounceback for this December? That will not be offered on a free dining bounceback offered this year. Free dining bouncebacks have been for the following year. Room discounts are for the current year. For free dining in this December, your best bet is to hope for a public offer.
You can however book bouncebacks for more than 1 trip. For example, you could book a trip for next June & December. I booked a split stay trip for September with the bounceback. Different dates even in the same week are counted as different trips.