When Ron Foster and Merry Anders set out on their journey to the House they are in a Chrysler, but arrive in a Plymouth. When they go to the estate agent
to collect the keys the Chrysler is parked outside, but they return to the house in the Plymouth.
When Joe returns from calling the sanitarium, he rings the doorbell because the front door is locked. Scott even mentioned that the door is locked as he goes to answer the door. When Scott gets to the front door, he doesn't even make any motion to unlock it, he just goes straight to the door and opens it without the key.
The movie placard or poster speaks of 13 keys yet shows a key ring with only 12 keys on it.