The train arriving at St Louis is a different train, as can be seen by the type of smoke stack on each.
When Mr.Van Rennselaer is talking into a voice tube to someone in another location, the background sound is of radio vacuum tubes being tuned in. Maverick was sat in the 1870's, vacuum tubes weren't invented until 1904.
Towards the end of the show the train pulls into St.Louis, the letters of the train line on the top of the passenger car are printed backwards. The film images must have been reversed.