Roger is seen snorting drugs in the disco, despite having admitted he had no nose when talking about his audition.
When Stan, Francine, and Michelle visit the Smith house under Communist control, the front door is hinged on the opposite side.
When Jane Fonda is scooping the cat food into the bowl, the paws decoration around the outside are white. Yet once the director yells 'cut' the paws are now black.
Taxi Driver was filmed in 1975, not 1974.
In Roger's office in 1974 is a picture of the Bee-Gees as they appeared on the Saturday Night Fever album, which did not come out until 1977.
During the flashback on how the present was changed, Hinckley's last name is misspelled on the name of his ice cream business. It is misspelled as "Hinkley".
The bulldozer that plows the Nativity scene makes the backing-up noise, even though it is moving forward.
Michelle is drawn without a black outline.
When Stan travels back to 1970, the sign over the front door reads 'The Smith's', making it possessive, and using the apostrophe incorrectly.
The slogan of the "Confusing Signs, Etc." store is "No, we're open", but the "we're" is spelled with a comma ("we,re") instead of an apostrophe.
In 1970, Roger is asked about his audition for Ryan's Hope (1975) which did not begin production until 1975.
Leonid Brezhnev couldn't have accepted Mondale's surrender because he died two years before the 1984 election.
Stan calls the gun he received as a gift from Michelle a 'Glock', while it clearly is not.