My wife and I once flew standby from RNO-LAS (non-stop on WN). We were the last two on a full flight, there was no overhead space available and we each left a bag at the bottom of the jetway as we boarded the flight. Each of those bags was accurately tagged to LAS -- I checked.

You guessed it: one bag made it, the other didn't. It came in on the next LAS flight.