The anniversary date is the day you bought your pet insurance. It'll be the same day every year as long as you don't make any changes to your insurance. If you make changes to your coverage, the date on which the changes become effective becomes your new anniversary date, and you have to pay a deductible when you make your first claim following this date. You need to know the anniversary date to know when the waiting periods end. However, there are no additional waiting periods if they've already ended by the time you make these changes.