What do you do when you receive late RSVPs?

What do you do when you receive late RSVP’s? On the invites it said you must reply by September 1st or bring a sandwich and a chair. Yesterday and today we received some. They aren’t even post marked until a few days ago so it’s not like they were lost in the mail. I’ve already don’t you seating charts, paid the caterer, advised the venue, etc. Do we call them and tell them sorry? Or do we re-do all of our work with the seating chart, send the caterer more money, etc? We were thinking we’d throw all the late people at one table and instead of a number call it the table of shame. That is if we do decide to let them come.