The appearance of Phillip and Arnold Drummond means The Fresh Prince of Bel-Air (1990) takes place in the same sitcom universe as Diff'rent Strokes (1978), The Facts of Life (1979), Hello, Larry (1979), and Silver Spoons (1982).
The visit by George and Louise "Wheezy" Jefferson means The Fresh Prince of Bel-Air (1990) takes place in the same sitcom universe as The Jeffersons (1975), All in the Family (1971), Maude (1972), Good Times (1974), Archie Bunker's Place (1979), Checking In (1981), Gloria (1982), and 704 Hauser (1994).