While I was disappointed with how ExpertFlyer chose to handle the coupon code I posted in the OP (saying it was "no longer valid" rather than full disclosure that they pulled it because it was supposed to be targeted), I was pleased that the recent e-mail I received announcing Seat Alerts included a 15% off coupon code. I will be using it for my renewal.
For those whose EF subscription has lapsed, make sure to carefully read the e-mails you receive from ExpertFlyer.