About 11 minutes in whenever Pete receives his phone call. After he gets off of the phone he makes a drink and leaves his office. The camera switches to an over the shoulder shot of Pete and we see a girl in a green blouse walk across the screen from left to right. The next camera angle is shot from Pete's left and we see the matched action of the girl continuing down the hall. Pete looks to the left and in the next shot we see the same girl in the green blouse walking through the open office area.
When Peggy visits her mother, on the table is a bottle of Cheerwine. Cheerwine is a soft drink that while has been available since 1917 is only available regionally in the Carolinas. Furthermore, that particular bottle was released as a 'retro' model in the 2000s.
The series is set in 1962. When the IBM typewriter is revealed to Peggy, it has a correction key. The correction key on the IBM Selectric was not introduced as an option until 1971, on the Selectric II.
While Don is in the Asian restaurant, Sukiyaki plays on the TV soundtrack. While the song was recorded as "Ue o muite aruko" in 1961 in Japan, it wasn't released in the US until 1963 - and the episode is set during the first week in March 1962 after the tragic American Airlines crash. Coincidentally, Sukiyaki was recorded by Kyû Sakamoto who later died in the crash of Japan Airlines Flight 123 on August 12, 1985.
The song used at Paul's party and over the ending credits, "Temptation is Hard to Fight" by George McGregor & The Bronzettes, was released in 1967. The episode takes place in 1962.
The date is 1962, a time when there was still segregation and discrimination, yet no one bats an eye when they see an interracial couple, something that would be scandalous at the time.
It was previously established that the agency couldn't afford to fire Pete Campbell because his parents were some kind of uber-rich who owned half of Manhattan, now they are portrayed as paupers with so little money that his mother can't afford a decent funeral for his father. In addition, Pete claims he knew almost nothing about his father which is contradictory to previous story lines.