Every single bride I've talked to said people RSVP'd yes but didn't come or didn't RSVP and did come. Every. Single. Bride. And now, it has happened to me! One guest asked to bring a plus one, which we agreed since people had said no. But, she hasn't gotten back to me to let me know if that person is coming or not.
Then, this weekend, I was talking to my FMIL who said her brother's girlfriend isn't coming anymore. MIL only found out because she emailed the girlfriend to say she was looking forward to meeting her, and that's when she said she couldn't come. She didn't tell me (and they were one of the first to RSVP!). Then, MIL mentioned that her (adult) niece might come. Her niece wasn't invited. She is the daughter of another brother. So, I said she could (since the girlfriend backed out) but that I would need to know. Why do people do this? At least this is before we sent the numbers in to the caterer so we can adjust them! But really, if you have to back out for some reason, please let the couple know!