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".
Leonid Brezhnev died in 1982 in the prime timeline, making it unlikely that, in the alternate 1985, Walter Mondale could surrender to him.
In 1970, Roger is asked about his audition for Ryan's Hope by a fellow employee at Elaine's, but Ryan's Hope didn't premiere until 1975.
Michelle takes Stan back to Christmas 1970 and causally mentions Jane Fonda is filming her Oscar Award winning film, Klute, which causes him to run off to find her. However, Klute wrapped filming on September 11th, 1970.
According to the DVD commentary, Jane Fonda, Donald Sutherland and Martin Scorsese were offered the opportunity to voice themselves only for all three to decline.