The Case of the Wayward Wife - S3-E13
Revealing mistake: Perry and Della step into an elevator but there is no line in the floor between the floor they are on and the elevator floor. It's continuous.
Perry Mason (1957)
1 revealing mistake in season 3 - chronological order
Starring: Raymond Burr, Barbara Hale, Ray Collins, William Hopper
The Case of the Sausalito Sunrise - S9-E19
Other mistake: The owner of a Los Angeles trucking company tells a driver who is going to San Francisco, "Take the San Diego Freeway toward Bakersfield." That freeway runs from San Diego to San Fernando. It does not go toward Bakersfield.
Hamilton Burger: Incompetent, irrelevant, and immaterial.