When Susie is on the phone in the lobby, trying to get Midge a gig, the man in the chair directly behind her appears and reappears during the phone call.
Chicken Fat Youth, played during Abe's morning exercises, was not released until 1961, but this scene takes place in 1959. However, the show occasionally uses anachronistic nondiegetic music.
Pauly refers to a "fun new font" on the camp newsletter. "Font" only came into common usage for type after computer menus featured the option. Prior to the 1980's, most people would have referred to a specific style of type as a "typeface." ("Font" would only have been used by typographers and graphic designers in order to refer to a specific weight and size of a specific typeface, e.g., "Times New Roman 12 point bold.")
The phrase "nerd alert" was not used in the 1950s and didn't become an idiom until the 2000s.
The opening parodies the film To Kill a Mockingbird (1962), which was not released until 1962, and the book wasn't even published until 1960.