Other mistake: When Ray is interrogated by Hamer, he states that Clyde drives nothing but a V8 Ford, but in the scene immediately afterwards, Bonnie and Clyde show up at his brother's house, driving a 4-cylinder Model A.
Factual error: In the scene where Bonnie gives Clyde the unloaded pistol through the jail bars, that gun was not manufactured until after 1972. It is a Bauer .25 ACP semi-automatic stainless steel pistol. Bonnie and Clyde's reign of lawlessness ranged from 1931 to 1934.