About 35 minutes into the show, the widow Mayfield climbs into her 1955 Ford Thunderbird convertible, clearly using her left hand to hold the steering wheel while reaching for the instrument panel with her right hand to turn the key in the ignition. All Fords in the 1950s and early 1960s had the ignition lock on the LEFT side of the steering column.
When the car is pushed into the river, the trim on the driver's side is only on the fender, but when it is being towed, the trim extends to the middle of the driver side door.
Claire Mayfield was driving a 1955 model convertible and it looked very new, which would make sense as she was quite wealthy. The time period was apparently mid to late 50's. When Roger Stratford enters his apartment, he turns on the table radio and the sound comes on immediately. Until the early to mid 60's the only transistor radios were handheld or very expensive options in cars. A tube radio takes a warm up period of approximately 20-30 seconds before there's any sound.
It's revealed that Ben Matlock's mom had died a long time ago, but in the pilot movie, "Diary of a Perfect Murder", it's established that Matlock's mother is still alive.