M*A*S*H - Bar Codes Aren't This Old
This slip up is in Season 11, Episode 14: Give and Take
At the part of the episode where Klinger enters post-op and gives every wounded soldier a bar of chocolate look when he gives the bar to the wounded North Korean. The Korean looks at the bar and even turns it over. At that point look under his finger and you can see a bar code with the lines and even the numbers. Bar codes weren't around back then I know for sure.