From what I have gathered from the past couple of years, and I can be completely wrong about this, but I don't believe they release the discount codes for december until August/September time frame-ish. Last year it was a general discount off packages (at least that's what I priced out, there might have been other discounts available). But there was no free dining.
When I called to price a vacation last year for December I told the CM I didn't care what days I was there just as long as it was X number of nights and had X MYW ticket and at a value resort with dinign plan. He said to me that he got a pop up, only had seen pop ups like this once or twice, but it was for Coronado Springs Resort vacation package at a price less than value resorts (it was like $69 a night or something, I can't exactly remember the specifics). I had to book it right then or I would lose it (we were not planning a trip for that time frame, I was just pricing out the discount they were offering) , so I turned it out. He said the offer was only good for as long as I was on the phone with him. I could not add the dining plan (he asked his supervisor) and it only pops up when you have flexible dates. (Just a FYI.)
