As he flees the blacksmith's, Bonnot shoots at Valentin damaging the windscreen on the car. The number, size and position of these holes in the windscreen changes between shots.
The Russian prince is called Volkonsky by some characters (and the credits), Bolkonsky by others. (The Bolkonskys were a genuine Russian noble family, while Volkonsky is a character in Tolstoy's War and Peace.)
Valentin and his team are driving Renault EK (the red one using during gunfight with Bonnot in the crowded place). This car was product between 1913 and 1916. As Bonnot was killed in 1912, this Renault was not available at this time. This movie is based upon famous 70's TV series "Les Brigades du tigre" where a Renault EK was also erroneously used by Valentin's team.