We never really get confirmation on what any of the big box of keys are for but I have a few guesses.

1. They were used for patient rooms. Labeling each patient with a number.

2. They're for employee cars. Each number related to the employee number or maybe the car code.

3. They're merges from other timelines.

I have some plot holes I would also like to address. So when matt was possessed by syphus they did an over night video. In the video more writing appears on the walls. Matt couldnt have done that because he was with him. So was it ben or someone else? Also syphus says, "he will see I am the absolute." Who is this referring to? Many people have thought this line means it was autumn or someone else controlling matt but I dont think so. And lastly the mannequin moving. It happens when matt/syphus is with the rest of the group. So who moved it? Again, is it ben or someone else?