When Kinsey mentions he wants his Star Trek spec script to be the following season's opener, Harry says it's not likely, meaning, that another season may not happen. That's because, despite the fact Star Trek would later become extremely popular, the show itself, that only lasted three seasons, had trouble in the ratings.
This episode takes place in December 1966.
Don and Megan are in attendance of the national premiere of "America Hurrah" at the Pocket Theatre on December 7, 1966.
Special guest return of Paul Kinsey, who was a regular character until the firm moved, and he was simply left behind when seeing the old Sterling-Cooper offices abandoned. Even before the decade turned into a hippie era, Kinsey was a beatnik progressive i.e. was ahead of his time.
At 31:31 in the bar with Joan, Don says "you know what this woman said to me once? 'I like being bad then going home and being good'". This was said by Bobbie Barrett in Season 2 Episode 3 "The Benefactor"