In an opening scene, as Betty comes in to her home she opens the exterior door to enter her house and, from the viewer's perspective (looking from inside to outside), the viewer sees an interior doorway where her front porch should be.
When Harry is talking to Sal, Ken, and Paul about needing someone to read scripts, the last shot of the scene reverses the negative of the film, as can be seen by Sal's and Harry's suit breast pockets and handkerchiefs being on the right side of their suits, instead of the left.
Don proposes the idea of placing Heineken end cap displays in the A & P's in suburbs like Connecticut. This idea is a big part of this episode's storyline. But Connecticut did not allow the sale of beer in grocery stores in the 1960's. Beer could only be sold in package stores.
When Don and Betty are having the Sterlings over for dinner, Don points out Betty's choice of beers: a box filled with Heineken bottles... with a logo that was not introduced until 1968, on a type of bottle designed in the 1980s. In 1962, the bottles would have been brown, and the Heineken logo was a red star on a yellow background.
When Don goes into the office kitchen late at night, there's a box of Mister Salty pretzels - a Nabsico product not introduced until 1966, four years after scene was set.