RSVP Organization

OK, after months of creating the perfect RSVP card, I am now stuck with the one dilemma that every bride worries about, what if my guest does not fill it out properly? I have seen before where there is a small handwritten number on the back of the RSVP, but after spending the time to carefully craft and design my RSVP's I didn't want to have anything handwritten appearing on them. So, I used my sleuthing detective skills and came up with a solution. I just bought an invisible pen! The numbers will not show up on the cards, but upon their return, I will simply use my new tool to detect the number in place. This way even if my guest forgets to put their name, I can revert back to my records and determine who it came from. Brilliant I tell ya!