Restaurants can change Dining for Miles requirements
Don't ignore those updated Dining for Miles books in the mail.
If you regularly dine at particular restaurants, check to see their requirements remain the same.
After I didn't get miles from a restaurant I eat at regularly, I found out it changed from awarding miles "anytime" to Sunday-Thursday.
One way to combat the Sunday-Thursday problem: Buy gift certificates during the week and then use them on the weekend.