How Does the Purge Alerts Work?

I have some Alerts defined to run everyday, keep 1 day, and suppress duplicates.  We'll eventually Keep for 7 days once it goes live, but for testing 1 day is enough to test on.  My issue is that although it is checking everyday and finding exceptions every day, it's not sending emails everyday.  I thought setting the Keep 1 days would keep duplicates from going out but after 1 day is should purge the history so in this situation it would allow it to send the emails every day -- eventually every 7 days.   But when I look at the