So, I thought that we would guarantee that people didn't RSVP with random people. Overall, we invited everyone with their SOs. I personally called a few single friends who wouldn't know a lot of people at the wedding and asked them if they wanted to be invited with someone. Still, today we received an RSVP that looked like this:
Jane Smith with the line next to will attend checked
Mary Smith with the line next to will attend checked
and a hand written "Plus One"
They weren't invited with a plus one. I also have no idea who this person is. How would I even do the place card if I decided to allow them this mysterious plus one? I was furious when I saw the RSVP. I would never assume I could just expand the guest list to someone else's wedding. I can't call them because this is from FI's side of the guest list.
Oh and we also received an RSVP with a post-it asking if someone else could be invited. WTF!