I hate to say it, but we go every year for 10 days. And I'm ALWAYS getting codes--postal (the best) and email. I think it depends on how much you are signed up for. We are registered with everything Disney and it's through different sources that the codes arrive.
Unfortunately, most of the codes are for when we can't use them. Or the wrong type of code. Yes, we're going in December, but the code I got was for a package. I got a code for Jan-Feb for room only and again for August-October for room only, but we couldn't go during those times. Oh well, sometimes it works out.