Retired Delta Airlines captain Karlene Petitt, who had a long-running dispute with her airline over her fitness to fly reported that a pilot from another airline, flying on Delta, noticed that the plane had incorrect safety briefing cards in the seat back pocket.
The flight was operated by a Boeing 757, but there were some seats with cards for a Boeing 737. The flight had to be delayed, eventually 10 incorrect cards were found, and fortunately this was in Atlanta and they had the correct cards to replace them with – otherwise the plane could not fly.