The PS3553 CASS report has two boxes with dates. The date in the B2 box is the oldest ZIP Code "validation date" of any address in your database. This date must be within six months of the date of the mailing for Standard or First-Class mailings and within 90 days of Carrier Route mailings. If it is older than that, your mailing could be rejected. Make sure that you have turned off all filters on your database by going to the Filters menu and choosing Clear All Filters. Then rerun the ZIP4 lookup on your entire database. This process will update the date in the B2 box to the current month.

Note: It isn't necessary, but if you want to locate which addresses are the oldest ones before rerunning the ZIP4 lookup on the whole database, go to the Filters menu, choose Set filters and then choose CASS Age. That'll find the records certified before a specified number of months.