Weirdest Invite Issue

Ok, so the other day, I came home to find that we had received an invite back in the mail from a cousin of mine that I haven't seen in a long time.

The weird thing? We received their decline to the wedding back at the end of August.

*blink blink*

I'm beyond confused, have no idea what could have happened, and wish I knew what was up!

It rung a bell with me because we accidentally referred to the husband of this cousin as "Steve" when his first name is actually "Dennis." That was pretty embarrassing. But the name was noted on the RSVP card, I sent a follow-up note apologizing for the gaff - "it's been so long...relying on other people to help...so sorry for the mistake and that we won't be seeing you in October!" - and hoped they would forgive the mistake.

But the invitation we sent to them was returned to us due to an improper address. And how the HELL did they get an RSVP card to RSVP with if they never received the invite in the first place?

It's Twilight Zoneish...

Could we have accidentally sent them two different invitations? In which case it's somewhat of a blessing that the USPS somehow delivered the first one but not the second one, because, OMG, do we really need to look like complete idiots to this cousin? "Hi, I know you already RSVPd that you wouldn't be able to make it, and I know we called your husband by the wrong first name and all, but really, COME TO OUR WEDDING!!!"

I don't get it. How did this happen?