Though the opening credit says 1890, the map in the Secret Service chiefs office is completely inaccurate. Some examples, the border between Texas and Louisiana is incorrect, Louisiana and Arkansas are shapes are not correct, Nebraska (admitted as a state in 1867) is shown as a territory and extending into Wyoming (which became a state in 1890), the panhandle of Oklahoma is missing, New Mexico is shown as a territory encompassing New Mexico and Arizona, but Arizona became an independent territory in 1863.
Towards the end when Velvet greets Chito in the saloon the boom mic shadow can be seen moving on the far wall behind the actors.