I think i'd have a major issue with people inviting people I didn't invite to my wedding. If you sent out formal invites with counts I'd only allow those who rsvpd with you to come. You may want to make a point to let the people who told you they invited others to let them know that you dont' want strangers at your wedding and that you would like them to attend but if they choose not to you understand and wish them a great vacation.