The address on the letter for the acceptance to the art school shows California as CA instead of Cal. CA did not go into use until 1963, when zip codes were introduced.
In an early scene, Perry Mason and Pete Strickland park their vehicles atop the Devil's Gate Dam. They get into a fistfight, exhaust themselves, and talk. It is daylight and not a single car or truck passes by. Although that is possible today (2023), that would not have been true in the 1930s. At the time, the road atop the dam was the main highway between La Canada and Pasadena. It would not have been possible to park and it should have been clogged with cars and trucks passing by. The road atop the dam was eventually closed to traffic in the 1950s when a four lane highway was built that bypassed it.
Melville Phipps tells Camilla Nygaard that he ensured an invitation was "hand-delivered to the embassy." The Japanese embassy, as are all embassies to the United States, is located in Washington, DC. (There are also embassies to the United Nations, located in New York, NY.) Japan has a consulate-general in Los Angeles.