On my first leg back home, I was sitting in my assigned seat when a nice woman in her 60s came up to me:

“Excuse me, I’m in 7B.”

Sure enough, her pass said 7B, but so did mine. The only time I had ever seen this happen was when someone got an upgrade to First Class. There was no First Class on this plane, though.
“OK, I’ll scoot over, and we can let everyone else sit down. We’ll then tell the flight attendant.”

This plan worked until 7C showed up. We explained the situation and the plan. She found an empty seat up front. No harm, no foul.

I was slightly confused. There was no way my pass was wrong, I printed it myself online. She had a gate-printed pass. Obviously someone had screwed up. As the door closed on the plane, I stared at her boarding pass and saw the problem. “Oh, I see. You have an earlier time on your pass than I do. Were you late?”

“Well, just what time do you think it is?”

I looked at my watch. It was still 3:40, and I had fully intended to catch the 5:00. The door closed, and the plane took off, and I’m writing this in the air. At least I’ll have a nice meal at IAH.