Factual error: This is a wardrobe error... in the next morning scene after William has been deflowered, he is still in his Fruit of the Looms, which have the name printed on the elastic waistband. Fruit of the Loom did not print their name on waistbands like this until the 90s, in the 70s they just had single blue and yellow stripes. (01:08:27)
Factual error: It's 1969 at the very start of the movie, and William Miller is looking through a bunch of awesome vinyl records that his sister has given him, including stuff from Cream, Jimi Hendrix, and Bob Dylan. In the stash is Joni Mitchell's Blue. Blue did not come out until 1971.
Factual error: In the radio station scene, the closeup of the turntable tonearm shows a P mount head-shell and Stanton 500 cartridge. Neither was available until the mid 1980s.
Factual error: When William runs into the street to look for Penny Lane, he runs between a row of taxi cabs. Across the street is a blue mid 90's model GMC Suburban. Since the scene takes place in 1973, this is obviously a mistake. It may be necessary to use zoom, depending on the size of your screen. (01:28:10)
Factual error: When the band is heading to New York City, there is a scene of them driving over a bridge heading into New York. In the background, you can very clearly see the Citicorp Centre Building. While the movie takes place in 1973, Citicorp Centre was not built until 1978.
Factual error: In a party scene, the song "Burn" by Deep Purple is heard. This tune is sung by David Coverdale on the "Burn" album which was recorded in November 1973 and was published in the beginning of 1974, so it can't have been played in 1973.
Factual error: In the Cleveland scene when the band is playing you can see the drummer is using a quad beater (the thing that strikes the bass drum) on his drum pedal. These were not available until the 1980s. Similarly the rest of the cymbal stands and hardware is far too modern.