In "The State Vs. Chip Douglas", Ernie finds his missing 1914-D penny when it falls out of his pocket. A close-up shows an Indian head penny lying on the floor. The problem is that Indian head pennies were not minted after 1909.
The series was filmed out of sequence; Fred MacMurray's scenes were filmed first, while scenes without him were filmed later on. This became evident when Dawn Lyn joined the cast as Dodie. Her permanent teeth were still coming in; as a result, her upper front teeth are barely visible in scenes with MacMurray and more prominent in scenes without him - often in the same episode.