The Case of the Cheating Chancellor - S9-E4
Character mistake: Paul Drake tells Perry the "speedometer mileage" of a murdered man's automobile is 63,192. Speedometers do not show mileage. He meant to say "odometer."
Perry Mason (1957)
1 character mistake in season 9
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.