All of a sudden, we have three! The first to come in, the top right in the front, appeared on 12/3/11. The second one, right bottom front, snuck in without us realizing it on Friday, 12/9/11. And the top left front has been showing the telltale dark spot on the gum for a couple days, and finally made it's appearance today.
The funny thing is that the one I was sure was coming in at Halloween was the bottom front left... which is the last one of this set to show up. Shows what I know.