Revealing mistake: After he's ambushed and killed in the alley, the "dead" sheriff can be seen breathing quite healthily.
Maverick (1957)
1 revealing mistake in The Forbidden City - chronological order
Starring: James Garner, Jack Kelly
Character mistake: Bret fires at "John Wesley Hardin" four times, but the doctor and all the witnesses say there were three shots.
Bret: My Pappy always said, "A coward dies a thousand deaths, a hero dies but one." A thousand to one is pretty good odds.