When inspecting the mine, Bill Every's flashlight has the blue-white light produced by LEDs rather than the yellowish light bulbs of the era put out.
When Cat is playing in the saloon, the piano tune she is playing is Maple Leaf Rag, which was not written until 1916. Earlier in the episode, Elizabeth tells the students the phonograph was invented 30 years earlier in 1877.
The song "You Made Me Love You" was sung and it was said that it was from a few years earlier. The song was actually not written until 1913.