Contrary to what is shown, the recording for "Good Vibrations" began during the making of "Pet Sounds", not after.
Dialogue suggests that the "Smiley Smile" album was completed by the Beach Boys without Brian's involvement; archival tapes show that he was actually very involved in the album's recording.
It is implied that Wilson dropped acid for the first time shortly after the release of "Pet Sounds". In real life, Wilson first dropped acid in the early spring of 1965, a year before "Pet Sounds".
Brian tells Melinda when they are sitting in the Cadillac in the showroom that his brother died two years earlier. Dennis drowned in December 1983. That would make the scene set in 1985 or early 1986. The song playing in the background is "Songbird" by Kenny G, which was not released until 1987.
In the studio, the baritone saxophone player is seen with a Yamaha baritone saxophone. Yamaha didn't make baritone saxophones until 1969.
Van Dyke Parks claims that he had been writing lyrics professionally since he was 14-years-old. While the real Van Dyke Parks began his professional career as a child actor, it wasn't until 1964 (at the age of 21) that he began taking an interest in songwriting and composing.
In a scene which presumably takes place in 1967, Murry Wilson tells Brian that he has sold off the band's publishing company. In real life, Murry did not do this until 1969.
Melinda Ledbetter is credited for inspiring the song "Love and Mercy", but in Brian Wilson: I Just Wasn't Made for These Times, Wilson says that the song came to him spontaneously after drinking some wine.
Murry interrupts the recording of "Caroline, No" to tell Brian that he predicts his new single "I Live for the Sun" will go to number one. By the time "Caroline, No" was written, "I Live for the Sun" was several months old, peaking at number 59 the previous year.
At the studio where the "Pet Sounds" recordings are re-created, the side entrance is handicapped equipped with concrete ramp and modern railing, along with the handicapped long bar "push" door handle on the interior of the door as seen when Mike and Brian argue. This would not have been installed until 1990 or after. Ramps used for load-in of equipment back in the mid-sixties, would have much less elaborate.
When Melinda and Eugene are talking outside about Brian, camera crew members are reflected on the side of Melinda's car.
When Melinda first meets Dr. Landy in his office, his watch reads 4:55 but his watch then reads 4:40 for the rest of the scene.
In the credits the listing for the song 'Sloop John B' says "Written by Brian Wilson". In fact Wilson's version was inspired by the Kingston Trio's 1958 version, and the song itself is a traditional folk song from the Bahamas. There is a transcription of the song dating to 1916..
When Brian jumps off the sailing ship with Melinda, he's wearing tennis shoes and plain white socks. However, when he walks ashore, he's wearing blue (or grey) socks.
When Brian talks about a Shanty album while inside the pool, by the end of the scene a crew member is reflected in the window behind him over his left shoulder.
When Murray Wilson tells Brian that he sold the rights to The Beach Boys' music, he states he sold the rights for $750,000. In reality, the rights were sold for only $700,000.
When Brian persuades Melinda to jump off the boat (near his house), he is wearing shoes, yet when they emerge on the beach he is only wearing socks.
During one of the pool scenes, Mike Love demands that he and Brian throw away the "Smile" lyrics and rewrite them as "normal" Beach Boys songs. In real life, some of those songs *were* rewritten for the "Smiley Smile" album, but they weren't any closer to being "normal".