A rare example of an historical inaccuracy from a later Mad Men episode (not that theres many anyway, but the majority occur in seasons 1-3), this one comes from the season six episode To Have And To Hold, set in 1968. Joan and her friend have a conversation about making reservations at the restaurant Le Cirque. Theyd have had a very long wait for a table, as it didnt open until 1974. Weiner initially joked that Christina Hendricks had ad-libbed the line, before admitting that it was a terrible error. Le Cirques publicist, meanwhile, commented that Sirio would have been open if he knew that Joan wanted a reservation in 1968.