Stupid random thought.
I was downloading some '50s TV shows to watch later. Most of the systematic Youtubers list old TV shows with numbers like S03E18 for Season 3, Episode 18. A few shows lasted long enough to need two digits on seasons, so this makes sense.
Would any radio or TV show need three digits? We're getting mighty close. Fessenden made the first known music and speech broadcast in 1906, but his station didn't last. The first 'solid' commercial stations started in 1919. It's possible
that one of those stations had a feature like Farm News that continued under the same title through the decades, which means a three-digit season number could be needed soon.
If you include Morse we'll get there sooner and more definitely. W1AW, the headquarters of ARRL, has a unique status as both broadcaster and amateur. It was founded in 1914, shut down during WW1 as part of the total tech mobilization
, then restarted in 1918. Since then it has been 'broadcasting' bulletins and code practice sessions regularly.
Some of the Navy's beacons may have been continously sending signals
longer, but you can't call their output broadcasting or programs.