When returning to the bar after the hunting trip, they are singing "Drop Kick Me Jesus (Through The Goalposts Of Life))" a Bobby Bare song released in 1976 after the Vietnam War had ended.
The hairstyles the men wear in the first scenes in the film, which are set in 1967, are anachronistic for their location, occupation, and socio-political orientation. While male hippies and rock musicians famously had long hair in 1967, it was unheard-of for patriotic steelworkers in Pennsylvania to wear their hair that long. Hair for that set of people is perfect for 1975, when the last scenes are set, or 1977-78, when the movie was filmed, but not for 1967.
The cans of Rolling Rock beer, Iron City beer (in the 1960s Pennsylvania bar), Pepsi and Mountain Dew (at the wedding reception), and Miller beer (in Vietnam) are all 1970s vintage. The bottles of Rolling Rock do, however, roughly represent the correct 1960s design.
When Nick enters the red-light district bar in Saigon, "Midnight Train To Georgia" by Gladys Knight and The Pips starts playing on the loudspeakers. However, this recording was not released until August 1973, at least 4 years after this event could have occurred.
When the guys sang "Drop Kick Me Jesus" at the bar just prior to the Vietnam scenes they were singing a song that would not be written until 1976.
When Michael returns from Viet Nam after a one-year tour he is wearing 6 service stripes - aka hash marks - on his sleeve. Each stripe represents 3 years of service.
Christopher Walken's character's Russian name Nikanor is misspelled as Nikonar in the movie.
"Stosh" is the Polish nickname for Stanley, not Russian.
The level of Michael's beer while he is leaning against the post at the wedding reception goes up after he drinks.
The deer that Michael kills in the hunting scene is not the same species as the one that is strapped to the hood of the Cadillac when the hunting party arrives back into town.
In the scene at the VFW hall where they are playing bingo, the guy calling out the numbers on the winning card calls B-15, but when the board comes into view showing the numbers that had been called, B-15 is not lit up.
In the first hunting scene as they're changing their clothes, Michael and Stan are arguing about Mike's boots. Nicky is seen putting on a sweater and had both arms in when it cuts back to Mike who delivers his "This is this" lines. When it cuts back to Stan and Nicky, Nicky is once again putting the sweater on as if it was never on in the first place.
In the bar before Nick, Steve and Michael are going off to Vietnam, Nick opens up the same can of beer twice.
In the bar, right before the guys start singing along to "Can't Take My Eyes Off You", Michael is sitting on a chair holding a pool cue in his right hand and tapping it on the floor. A split second later as they begin to sing, he pounds the cue stick on the floor with his left hand.
When Angela looks at herself in the mirror wearing her wedding gown, a mic hanging over her head is also reflected in the mirror.
During a brief moment, the whole camera crew becomes visible in a shop window.
The hunting scenes supposedly taking place in the Appalachian Range are obviously filmed elsewhere: The Appalachians are a smooth rolling range, but the scenes show towering, jagged peaks. The scenes were filmed in the Cascade Range, clear across the country.
The deer that Michael shoots is an Asian Red deer and not indigenous to North America.
When Michael comes back from Vietnam he has a full beard while in uniform. He would not have been able to leave Vietnam in uniform until haircut and facial hair complies with uniform regulation AR 670-1.
Mike wears the green beret of the U.S. Army Special Forces operator. He is dressed in SF tigerstripe camouflage in Vietnam. However, in full dress uniform his left shoulder sports the 101st Airborne Division badge.
The religious ceremonies are held in a place marked Russian Orthodox Cathedral. A cathedral in any religion is the seat of a bishop, usually located in the population center of a diocese. It is unlikely that such a place would be located in a small town such as Clairton.
When Michael goes back to Vietnam to find Nick, it is obviously in April 1975 as the fall of Saigon is depicted. At Nick's funeral, Angela's son is no more than 2 years old, yet Angela had yet to give birth when Mike, Nick and Steven left for Vietnam. That would mean they went to Vietnam in 1973...however, all American troops were withdrawn from Vietnam by March, 1973 let alone engaging in combat missions and being as prevalent as shown in the film.
Steve and Nick, while depicted as assigned to 101st Airborne Division, they were shown wearing Marine's M1955 flak vest with a rope ridge on the shoulder.
In race scene with truck, a state of Ohio route sign is seen on pole.
When Nick walks out on the prostitute, she picks up her child and bumps its head on the lampshade.
When hunting, Michael carries a left handed Winchester Model 70 rifle, with the bolt handle on the left side. However in one shot during the second hunting scene, the bolt handle is suddenly on the right hand side. His wristwatch is also on the opposite wrist. The editors apparently flipped the negative so that he would be facing the right direction to match the other shots in the sequence.
In the bar scene at the beginning of the film, a supposedly live football game on the TV is obviously film, complete with many scratches on the image.
When Linda goes to Mike and Nick's trailer for the first time, the trailers hitch as well as the tail lights can be seen. The wires from the tail lights are seen running into the windows above the hitch. The tail lights should be on the rear while the hitch is on the front.
Right before Nick's funeral, the scene shows the Eagle Super Market with the exact same sale signs in the window as at the beginning of the movie, which were different when Michael had returned home from Vietnam, some year-and-a-half later.
When Nick is killed in the final Russian Roulette game, the gunshot is underneath the flow of blood on his bandana, yet on the close up, the gunshot is near the top of his bandana while the flow of blood is underneath.