Ingrid Boulting's hairstyle changes between the scene with the performing seal and the scene at Monroe's uncompleted beach house.
At Cecilia Brady's place she has photos on her walls of herself with obvious 70s style hairdos and she is posed quite unlike the 1930s. They seem typical of 1970s fashion shoots.
Stahr uses a telephone with a spiral cord in several scenes and telephones with spiral cords are seen on his desk. Spiral cords weren't introduced until the late 1950s.
When Robert De Nero as Stahr enters his residence for the first time, he refers to his Butler as "Kino", which is the actor's real last name.
Brimmer eats multiple cookies with coffee - during the meeting between Stahr and Brimmer, they are served coffee first, then a tray of cookies are served, from which Brimmer takes 1 cookie. Over the next several moments, Brimmer eats 2-3 cookies though he clearly only took 1 cookie from the serving tray.