Check it out. They are actually admitting that the course was incorrectly certified.
That wasn't so hard, was it?
Based on this new information, my actual pace per mile was 11:54.
Update: The viewing audience ought to know that Lindy and Roisin alerted me to this story as it was developing. Don't I sound all newsy and stuff? Anyway, Lindy pointed me to the Runner's World forums, which are a little intense, mind-boggling, and memorizing (I mean, I thought I was obsessed). Reading through the discussion thread about the CDC course and the comments that knowing John Bingham, he would come clean if something were amiss (unlike another race organizer), I decided to check the CDC Web site to see if it was official. And, low and behold, it was.
When I first read on Roisin's blog that her Garmin was showing a longer course, I realized that... hmmm... it did seem as though I slowed down significantly between mile six and seven. So there you have it.