My daughter actually wanted to have wording on the RSVP stating the number of people actually invited, but her FH thought it would not be proper ettiquete, and I kind of agreed with him. In hindsight, and seeing all the posts regarding uninvited guests, I would recommend that type of wording be on the RSVP's.
I recently saw an RSVP card with the following wording that made it perfectly clear how many people were expected: "____(#)__-- of place settings have been reserved in your honor."