Originally Posted by ExpertFlyer Voice

The alerts check on a varying schedule, several times a day at minimum increasing as the day and time of departure gets closer. However without knowing the details of your alert we can't tell you what happened.

The best way to check to see if you would be alerted at the next check of the alert is to run a Quick Check from the View Saved Alerts page when you see the inventory. If the Quick Check tells you that it found availability, then you will be emailed at the next scheduled check of the alert, if not, then there is something wrong with how the alert was setup.