Simo is beat up easily and hit with a chain. His injuries get better and worse from scene to scene. Most notably, when he finds a cigar and confronts his ex-partner. In that scene outside Chips, he is strong, moves easily, and has no injuries on his face at all.
As the detective with Simo at Western Costume walks down the stairs, his hands are at his side. Just as he leaves the building, his hands are now in his pockets.
In 1958 it shows George Reeves burning his Superman costume after he hears the show was canceled. But in reality Adventures of Superman (1952) was never canceled when he was alive. There had been a one year hiatus and then it was renewed for another two years, to begin in 1960.
During on-the-set scene of George Reeves "flying" during filming of Adventures of Superman (1952), background music is playing on set. Except for playback on musical numbers, there would no need for canned music on set as it would be added later.
When Louis Simo is entering the Mannix house behind the flower delivery man, the flowers' ribbons read "Eddie and Toni, Happy Anniversary." Their anniversary was on May 31, George died on June 16. In that scene, Toni was grieving George's death. Unless they were celebrating their anniversary two weeks late, this is an error.
In the Spring of 1951, when George and Natividad see Rita in the club, she is obviously pregnant. However, Rita Hayworth's last child, daughter Princess Yasmin Khan was born December 28, 1949, from her third husband, Prince Aly Khan.
Simo is driving his son "to school" in late June when school is out for the summer.
When Simo drives his son to school and presents him with the gift of the Etch A Sketch, his Chevrolet's steering wheel is clearly is never correctly in the center position although he shown to be driving straight. This suggests the car is being towed on a trailer while being filmed.
It is 1959, well into the golden age of broadcast television, yet there are virtually no television antennas visible on the roofs of any of the houses in the shots of the "period" neighborhoods.
The elevators in the hotel lobby have LED displays above the doors (to show the floor number). These were not developed commercially until the mid-1960s and did not become common until well after that.
When Louis Simo returns to Mrs. Bessolo's hotel room and finds that she is no longer there, the door across the hall has an electronic key card lock.
The liquor bottle that Louis Simo drinks from in one shot is seen to have a UPC bar code, not developed until the early 1970s.
The Los Angeles police cars seen at the beginning of the movie
outside Reeves's house are from the time period, however, the red rotating warning light on the roof is inconsistent with LAPD use at the time. The LAPD cars had the two barrel lights with a siren mounted in between them on the roof. This type of warning system was used until at least the late 1970s-early 1980s.
When the child points the gun at George Reeves to see if the bullet will bounce off of him, you can hear the hammer being cocked back and the hand motion of the child also indicates he is cocking the gun. However, the gun is shown from then on with the hammer in the forward position.
There were no Esso stations in California at that time. They were known as Enco stations in that state.
Suspicious that her son is actually a murder victim instead of a suicide, Reeves's mother takes a train from Illinois to California and somehow manages to arrive in Los Angeles and consult a private eye before news of the tragedy is even announced in newspaper headlines.