Ricky's Old Girlfriend - S3-E11
Continuity mistake: When Fred tells Ricky there's an article in the newspaper about Carlota Romero, there's a closeup of the newspaper's back page with Carlota's photo, but later when Lucy takes the newspaper (the same NY Gazette issue) from Ethel, before she turns it over we can see that the back page photo and layout are different. (00:08:30 - 00:10:20)