Update on the mystery show that originally aired in 1975. It's called Ellery Queen (name of the main detective) and was sent to me on disc by my mom. I have since confirmed that she watched it on tv when it first came out.
My general love of mystery shows comes from watching a wide variety with my mom, definitely including all the PBS stuff as a kid.
It took a bit of time to settle into the conventions of the era, but it's actually fairly progressive for the day and age.