At 52', the length of Jeanne's cigarette ash is not consistent between shots.
When Mesrine returns to Canada after his arrest in the USA he is shown on an Air Canada Caravelle, an aircraft never flown in real life by Air Canada.
The Canadian prison tower guards are armed with Ruger Mini-14s, which weren't introduced until 1973, though the escape occurred in 1972.
The American DVD release boasts of how Mesrine's criminal escapades covered three continents, which confused audiences because the film only shows his work on two continents-Europe and North America. The filmmakers cut his brief sojourn to Venezuela out of the story, likely because he didn't do much there. He stayed for a few weeks after leaving Canada, but before returning to France.
When Mesrine & Mercier are standing on a the roof of the building in Montreal, you can see cars/trucks/vans on the street, you can clearly tell they are modern vehicles and not ones from the '70s when this is supposed to take place.
As Jean-Paul waits on the platform of the Montreal metro, a "Stand clear of the doors" sticker can clearly be seen. These were only introduced in 2001.
The ballistic vests are clearly not the ones are used in the 70s.
At the Bonaventure metro station scene, when the metro arrives, a sound of the wheels screeching can be heard as the train stops. The Montreal metro has rubber wheels, so it normally stops silently.
In the Monument Valley scene, while the helicopter is filming backwards up to the hill, you can see all the silver-colored trailers from the film-crew on the left side.
At the metro station in Montreal, the man is standing in Sherbrooke station smoking, but as the train arrives, the footage is from Bonaventure station.
At the roadblock in Monument Valley, the film stated it was in Arizona, but the scene was filmed just south of "Forest Gump Hill", in Utah.
The prison's siren is not triggered when it is attacked by Nesrine and his comrade.
Guido does not turn his head or try to hide immediately when his comrade is shot.