Yeah, a few of our engagement invited went missing too! I don't think she'd have posted them yet, we're still 10 weeks out, or so.
We had another really interesting situation earlier this year. I was talking to a friend about someone who invited herself to our wedding (complete with the phone call to say "So, what time does the ceremony start?") and this other girl was saying "God, I would NEVER go to something if I hadn't got an invite" Meanwhile, her engagement party was 2 weeks later, and we hadn't got the invite, so just didn't go. When our friend found out, she was devastated that we thought we hadn't been invited (or she acted really well!) but remembered the conversation! We laugh about it now.