Had it once going to LAX. Was in 83A getting ready for a lovely stint in WT. Another chap came over and told me I was in his seat.

My boarding pass showed 83A, as did his.

Crew opened their iPhone and the other gentlemen - whilst holding a BP for 83A - had been moved to 63E (WT+).

Now whilst I can appreciate an upgrade is an upgrade… that’s an upgrade I’d politely decline!