At the 15 minute mark, two man are seen walking up a set of stairs in close up, where the steps have aluminium edging. It was not until the late 1960's that aluminium was introduced as edging for stairs, and not popular until well into the 1970s.
In the opening scene of the movie, two US citizens are attempting to cross the border from Canada into the USA and are asked, "are you carrying any guns or alcohol?', during the time setting of this movie and many decades well beyond, export of alcohol and guns from Canada to USA was legal and without any border taxes or tariffs. So the question asked by Canadian officials at the border would not have happened.
In the movie, Brian Stuart Boyd who plays "Don", is seen frequently wearing a straw "fedora style" hat that has an obvious polyester or nylon hat band. Polyester was not invented until 1935, and nylon, not until 1941, well after the time setting of this movie. which is pre 1930 when prohibition ended..
Near the end of the movie, when the plane crashes, a close up of the engines shows "die stamped" into the alloy on a cylinder head is "Quibesan" which is not associated with any engine manufacture nor of any type of machinery. Is this an "easter egg"? Also, spark plug covers shown in that shot are silicon, which did not replace rubber and come into use until decades later.
Near the end of the movie where a red bi-plane is coming in to land, the film shows the plane banking around to avoid ground fire, but now the plane is yellow in the shot.
In the opening scenes, border patrol officers are seen firing rifles into the river. As they reload each time they fire, no spent cartridges are ejected.
At the 1 hour,14 minute mark of the movie, a show girl is seen wearing a suede jacket with a nylon zipper. The zipper did not come into use until the 1940's, while the nylon zipper did not exit until the 1960's. Also, a "show girl" who would wear the latest fashions, so it is highly unlikely she would be wearing suede with a zipper in the 1920's, given that suede was not a popular fashion item until the 1970s.
At the 1hr. 7 minute mark, protagonists planning to assault an incoming plane are seen sitting in low grass while wearing white shirts amid green grass at the path way of the intended landing area. Even blind Freddy would have seen them.