Here's what happened to me.
I booked a AAA vacation in October for 1st 2 weeks in May. Waited for codes and low and behold we finally got some. I went to have the code applied to my ressie 5 times and each time WDTC came up with a different amount ranging in $ from 2000 more than AAA to $45 less.
Then it struck me that I would have to cancel my existing ressie to get the code applied and when I called to do so (another 3x) STD rooms were no longer available and it would cost me more than my AAA rate. Finally I got a CM to co-operate but I was one day too late. I had to pay my trip in full 45 days before arrival (WDTC rules) and the cancellation/change fee cost more than the saving I would have made.
I shouldn't be too upset as I did save about 10% off rack using AAA but it was a frustrating experience.