We had an invitation returned by the post office yesterday, because of a wrong address. It took nearly a month from the time I mailed it to make it accross the country and back. Since it's FI's high school friend and his wife, I asked him to contact his friend, explain what happened, give them the wedding info so they could plan to attend if they like, and get their correct address so I could mail the invitation. From comparing what we got back to my spreadsheet, it appears we had the right address but a 6 got flipped to a 9 when we addressed the envelope, and I failed to double-check. They at least got our save-the-date (which had a link to the website, with time/location/hotel info), and had at that time told FI that they would try to make it, but it is far to travel. I feel bad, because the late invitation certainly doesn't help them with planning for that sort of travel, and I can see that sealing the deal of them not coming.
I was thinking of including a handwritten note with the invitation, apologizing for the mix-up, saying we hope they can still make it, and acknowledging that the RSVP deadline on the card (likely) will have passed by the time they get the inviation but we have a couple more weeks before we need final numbers and they can contact FI directly if they are more comfortable with that. Is any part of that appropriate? Should I just leave out the last part and have FI relay them that message directly? Should I stay away from all special notes entirely? I just feel so bad that we messed this up, and I'm not sure if there is an etiquette-approved way of remedying it. What would you do?