Factual error: In the opening shot of the city of Verona, it is possible to see a bicycle moving in the distance. Bicycles weren't invented at the time the film takes place.
Factual error: Rosemary calls Dr. Hill from a pay phone and says, "The baby's due on Tuesday, you remember you told me June 28th" (and June 28th 1966 does fall on a Tuesday). In the previous scene in Dr. Sapirstein's office his receptionist is making an appointment "next week" for a patient and that date is "July 10th" indicating that if Rosemary is due on June 28th (which she says is next Tuesday) the dates do not match and it must still be the week of June 20th which is at least two weeks before July 10th. (01:44:45)
Factual error: In the famous tugboat scene, Fannie rides out on a New York Central tugboat painted jade green - a color which wasn't instituted on the boats until the early 1960s. To be accurate, the tugboat would have to have been painted red with a black stack and the New York Central logo.
Factual error: The film tells the stories of five male/female couples. They have conflicting aims in their relationships. For example, one wants to become a parent while the other does not want children. Thus they all obtain supplies of contraceptive pills (in bottles) and re-label them as aspirins or vitamin tablets (or vice versa) depending on whether they want pregnancy or not. The bottles get mixed up, causing panic and anxiety for all involved. All the interlocked stories are based on a complete error. Contraceptive pills are not stored in bottles. Contraceptive pills are packaged in 'blister packs'. This basic fact makes a nonsense of the entire film.