In Susie's photo album that her father flips through, there is a picture of a Smurf figurine at the top of the right page. While Smurf figures were around in the 70s, that particular Smurf (a singing "rocker" Smurf with a microphone) wasn't released until the late 1990s.
Earlier in the film(prior to Susie's murder), Abigail is seen reading several paperback books (including Herman Hesse's "Steppenwolf" and "Dr. Spock's Baby and Child Care") that have bar codes on the back. Bar codes for products were not in use until 1974, one year after the murder occurs, and were not commonly used in most stores until the late 1970s.
The split-level houses along Bryan Ave in Malvern, PA were built around 1957. In the mid seventies, they all would still have had wood prime windows with exterior metal triple track storm and screen windows. However, George Harvey's house and the one across the street have thermo-pane replacement windows.
George Harvey had to have dug out a rather large amount of earth to build the underground room where he murdered Susie. When we see him luring Susie into the room there is no pile of dirt anywhere in view. He would have also had to use the dirt to fill in the hole after dismantling the room. Where did all of that dirt go?
Vietnamese immigration was limited to families of servicemen prior to 1975, however, there are almost no details given about Holly's character; there is evidence to contradict that she had a serviceman parent as she does not have an Anglo family name.
Susie is killed the 6th of December. In Pennsylvania, by December there would be little to no foliage left on the trees by then, yet when the detectives go from home to home, you see full trees and some with autumn leaves-more like a day from early October.
When Abigail and Richard are in bed, we see that Abigail is reading Exile and the Kingdom by Albert Camus. As Richard begins to kiss her, she is seen reaching toward the nightstand to place the book on top of a pile of other books, including Siddhartha by Herman Hesse. In doing so, she accidentally knocks both books to the floor, but in the next shot, as she reaches over to turn the lamp off, Siddhartha has reappeared on top of the pile of books on the nightstand.
During one scene Jack is holding the ship-in-a-bottle that he and Susie made together near the beginning of a movie. In a subsequent shot he is shown busting the bottle (and many other bottles) against the desk. However, in a later shot he is shown holding the same bottle as he shrinks to the floor crying.
When Susan meets Ray and opens her locker we see the imprint "Fairfax Public Schools." Later in the movie she identifies her location as Norristown Pennsylvania. Later when George Harvey is looking at a scrapbook there are numerous references to Fairfax Virginia printed in the newspaper articles.
Just for the record, there is also a Fairfax HS in Los Angeles, California, which would make the Vacaville reference make more sense.
That still leaves the question of the changing leaves and snow on the ground, but Fairfax VA is not the only town by that name with a high school.
When Jack Salmon is lying in the hospital bed we see a ventilator operating, yet Jack is not intubated and is in fact only wearing a simple free flow O2 mask. The ventilator would not operate without positive pressure to act against.
Susie says, "I was murdered on the 6th of December 1973." The 6th of December was a Thursday in 1973.
When the detectives go to question George Harvey, they ask him where he was last Wednesday. His whereabouts aren't important on that day because Susie was murdered on a Thursday.
We see corn fields in Malvern, PA. There have never been corn farms in this area. If there were any type of farms in this area they would no longer be in existence when this movie takes place. By the 1970s this entire area was developed as housing subdivisions.
Jack starts developing Susie's 24 rolls of film at the rate of one per month about 6 months after her death. However, according to the article in Harvey's scrapbook, it is at least 4.5 years after Susie's death when Jack collects the final roll.
The day that Susie is murdered is said as being December 6th, a Wednesday. In 1973, December 6th was a Thursday. The family is watching "The Partridge Family" and it is light outside. "The Partridge Family" was broadcast on Saturday nights at 8:00 Eastern (7:00 Central Time) and in December well after sunset.
When George Harvey is looking at the scrapbook he has on Lindsey Salmon the first article refers to Lindsey receiving a soccer award on Saturday the 9th of May. The 9th of May occurred on a Saturday in 1970 and 1981 which is incorrect in the context of the film. Furthermore, if one closely examines each of the supposedly different articles they each contain the same exactly phrased paragraphs though in different arrangements, sometimes very incongruously (such as an article about her sister's soccer award containing exactly the same paragraph about a helicopter search for her missing sister as in a previous unrelated article).
The goof items below may give away important plot points.
When Lindsey is sneaking around in George Harvey's house, she is wearing an old style of Nike running shoes that were introduced in the 1980s. But the events in this movie were supposed to have taken place in the early to mid 1970s.
During the final scene as the sister is chased out of the house you can clearly see that is a fall day. The next scene (after the mother returns) you can see snow falling as the cops arrive. The scene after that shows a fall day while the safe is being dumped
In Susie's flashback, you see Mr Harvey dragging her cut up body into the safe with all his clothes on. His clothes were clean and contained no blood on it, yet we saw Susie watching him clean up all the blood and mud in his bathroom after her death. He is then seen getting rid of or cleaning the dirty clothes
After Jack has been beaten up by Brian in the cornfield we see that several more buttons on his shirt have come unbuttoned but in the next scene where he is being rushed through the hospital, only the top button of his shirt is unbuttoned.
Grandma Lynn drives Lindsey by Mr. Harvey's house and there is snow covering the ground. Next scene Lindsey is jogging by with her teammates and gets a cramp just before breaking into Mr. Harvey's house, there isn't any snow on the ground, just leaves. Then next scene she shows the scrapbook/evidence to Grandma Lynn and when the police go to Mr. Harvey's house there is snow covering the ground again.
When Lindsey breaks into Mr. Harvey's basement, she knocks a stack of bundled newspapers to the floor. While the stacks are not seen in the close shot on the broken glass when Mr. Harvey checks the basement, the stacks of bundled newspapers are shown in the lower left corner of the screen in the next shot of the basement floor which is a wider view.
George Harvey is shown looking at newspaper articles including one about Lindsey's graduation in the Class of '77 / '78. Subsequent to this scene, Jack is assaulted by Brian in the corn field. Brian was in at least the same school year as Susie who is older than Lindsey yet the newspaper article Lindsey subsequently finds when breaking into Harvey's home says Brian was a senior at the time of the assault. Also, Lindsey is shown running with a school team prior to breaking in when, according the previous article, she would have graduated already.
The safe in which Susie's corpse is hidden obviously weighs way too much for a single person to move, yet the killer somehow manages to move it out of his basement and into his car without anyone's help and within little time.