I asked this question a month or so ago and most of the responses were that they do not contact you. You technically are not renewing your DDE card each year. You're just getting a new one.
BTW, effective Jan 1 the DDE card goes up to $60 for AP holders and the second card will now cost $25. My DDE expires 2-26 but I called yesterday to re-up so we could get it at the 2005 cost of $50 with no cost for the second card. I know I'm losing a couple months, but next year we're going in June and Oct so it doesn't really matter for us.