My blues band was doing Joe Cocker's arrangement of "The Letter." The record is in Bbm, but we had been doing it in Am. This was right at the edge of the new female singer's range, so she asked if we could do Dm. At the next rehearsal we quickly ran through it once in Dm without the singer, who couldn't make that rehearsal. All was well.
The next gig comes up and we get to "The Letter." Bandleader had printed setlists with keys, but didn't change the key of this song on the list from Am to Dm. So the list says Am, but we just rehearsed it in Dm for this singer, and........BL crossed out the key on my (and only my) setlist and wrote Cm for reasons unknown.
The band started the song in three keys simultaneously.