When Abe and Peggy are arguing about whether they should stay in their apartment (33:29-34:44) Abe's shirt switches back and forth from being partially and completely unbuttoned.
When Henry is eating in the restaurant with Betty and Don walks in Henry is holding a cup. The camera angle changes and Henry is no longer holding the cup.
On his way to Bobby's camp, Don pulls into a gas station and tells the attendant to "Fill it up with Regular." 1960s era Cadillacs required Premium gas.
At 32:07 Don is lying in bed with Betty when he says "If we'd lied here together with you in my arms..." which is an odd mistake for a wordsmith like Don to make. It should have been "If we'd lain here together..." .