The exchange certificates do not have a 12 digit number, however they do have a bar code with about a 16 digit code under it. What's weird is if you look at the will call codes they also utilize about a 16 digit code, not a 12 digit code. If they can link the will call codes, why not the exchange certificate codes?
I'm going during Thanksgiving, and if I have to wait to schedule my FP+ until the day we get to WDW, I'm going to be upset because I'm pretty sure that I will not be able to access any of the main attractions at the times I want because the fastpasses will already be picked over.