There's this episode (https://cheers.fandom.com/wiki/Woody_for_Hire_meets_Norman_of_the_Apes) where Woody was a crowd extra on Robert Urich's show Spenser for Hire (which was actually shot on-location in Boston, where Cheers was set) and Urich himself made an appearance. I ask this because Cheers was of course, an NBC show while Spenser for Hire aired on ABC. I don't know how common it was for a show on a rival network to serve as a big part of you're episode's storyline (instead of being a throw-way joke).

maybe competing networks do favors for each other so both get a perk