I am an idiot.
At least, I was apparently an idiot on January 21st of this year. I finally got hold of a live human at the airline so that I could have them find my missing airline reservation for the cruise. I gave him my credit card number - no joy. I gave him my confirmation number and name, and he found the reservation just fine on his system. Yep, absolutely perfect. A reservation for a flight leaving Denver and flying to San Diego around 6:00 pm on Friday the 12th.
I booked the wrong month and - obviously - missed the flight altogether.
The customer service rep was very gracious, and the airline had held my reservation as unused credit, so I was able to apply it toward the correct flight on March 12th. Granted, I had to provide some additional cash to get on the new flight, since the cheapo fares had long since been exhausted, but I have a seat and the additional cash is a reasonable price to pay for idiocy.
I don't know what made me try to do the early checkin the other day, but I am incredibly glad that I did it - just think what might have happened if the first time I tried to pull that reservation was 24 hours before the flight!