This is an add-on to the previous post. It occurs to me that the Mad, Mad, Mad Comedians special-pilot starts with and really features the Smothers Brothers…who at the time this aired (4/70) had been booted off CBS despite pretty good ratings. This leads me to suspect that the show was produced at least a year before it aired. I mean, if you were a TV producer, would you want to be shopping around a pilot starring two guys who'd just been kicked off network television because right-wing advertisers didn't want them on? The Brothers went off in September of '69 but their cancellation was final some time before that and looming in the previous months. Also, a year or so before, Flip Wilson was pretty hot and all the networks were courting him for a series. His NBC one went on the air in September of 1970.
Within the animation industry, there was a long, checkered history of proposed cartoon shows built around the Marx Brothers. For a time there, every time I turned around, a different producer either had the rights, thought he had the rights or was pitching the idea with the hope that he could secure the rights. My friend Earl Kress wrote an entire pilot for Filmation and not long after that failed to go anywhere, I was approached by another producer (not anyone you've ever heard of) who said he was "making a deal" with whoever you'd make a deal with for such things. He wanted me to write the pilot for his Marx Brothers cartoon series but there was a catch: No Groucho. He had the rights to use Chico and Harpo and he thought he could get Zeppo ("How expensive could he be?") if I thought Zeppo's inclusion would make up for the absence of the guy with the mustache. I told him it would be like hearing "I Heard It Through The Grapevine" performed by Pips only.