I happened to be watching part of the movie "Ray" on HBO a couple weekends ago and had to chuckle at one scene which was supposed to be in the 50's. The scene was on a highway with a railroad overpass, in which a modern double stack train was slowly crossing overhead. Looked pretty out of place with all those 1950 era vehicles passing underneath! My wife says, leave it to you to pick out something like that! Most people wouldn't even notice something like this, but to me, if a movie scene is to be accurate, they should pay attention to all the details of the scene. How hard would it have been to round up some old boxcars that, even if they were somewhat newer than they should have been, would have been slightly less noticeable. However, even they should be lettered for some fallen flag railroad like Southern, L&N, or something of that time, not today's NS or CSX! What will we crazy railfans find to complain about next?
Even in movies with much closer time intervals between the "period" depicted and the time of filming, incorrect props creep in. A favorite non-railroad example is "They Were Expendable", the 1946 movie about PT Boat Squadron 3 in the Philippines at the beginning of World War Two. The armorer did a pretty good job, there isn't an M1 Garand rifle to be seen because they hadn't been issued yet in late 41 / early 42 time frame the movie depicts. But the PT boats themselves are wrong, ELCO 80 footers and Huckins Boats in place of the ELCO 77 footers used by Squadron 3. There apparently weren't any of the correct early ELCO 77 footers left in the Florida training squadron, where the movie was filmed, by the time it was done in 1946.
The situation is very similar in the use of railroad equipment in movies. You can re-create just about anything if you are willing to spend enough money to do it, but it is worth it for a couple seconds in the background of a scene?