Best romance movie mistakes of 1978
Factual error: At Professor Jennings' place, the stoned Boon and Katy sing "Hey Paula." The song was only pressed in November 1962 and didn't break into the charts nationally until late December of that year, whereas the scene depicted takes place sometime in the autumn of the same year, before the song would've even been recorded.
Continuity mistake: In the scene in the Beatles hotel room where Nancy Allen comes out from under the cart with the cokes on it, when she first sees the Beatles' guitars, notice that in the very first scene, the Hofner bass is left handed (the pick guard is on the left as you're looking at it), then it cuts to her, then when it cuts back to her rolling on the floor with the bass, it's suddenly right handed, then when in the last scene with her handling it, it's left handed again.
Continuity mistake: Near the end of the film, when Richard Gere and Brooke Adams is by a boat and attempt to escape up the river, Gere is shown waving a kerosene "barn lantern" to illuminate the boat. In a slightly later shot, he is doing the same thing, but the lantern has become a Coleman gasoline lantern. These lanterns had not been invented yet in 1917, the year during which the scene in question takes place.