Factual error: When Richard and Elise are walking down a hallway, he asks when the acting company will leave. Notice the two doors they pass on their left. The doorknobs are modern replacements with large, shiny brass plates that reinforce the door for better security, commonly retrofitted during 1960-1980 in public buildings with older "skeleton key locks". They are seen during the 1980 scenes, but in 1912 they should not be there. Interior locks of that era usually had smaller plates, like the one Richard first sees in the occupied guest room.
Factual error: In the final sequence, Richard Collier is shown sitting in a chair where, as others break into his room, we are lead to believe "he had been for days". Yet his hair is clean and combed, his clothing seems immaculate, and apart from some makeup, he shows no sign of any mental or physical problems.