As you are sending out your invitations, you most likely are working with a list or spreadsheet to keep all the names, addresses, and replies in one place.
Consider adding a column to your list and assign a number to each guest.
When you assemble the invitations to go out, write each guest's number on their RSVP card. It doesn't have to be big or obvious, just a little thing in the corner. This way when the RSVP comes back, if you can't read the handwriting, are unfamiliar with the name responding, or if someone had a name change, you can more easily determine who on your list the RSVP belongs to, saving you time and frustration.
Bottom Line:Taking a moment to add one little number to your spreadsheet and each RSVP card can make your RSVP management much simpler and more organized.