combinations and how you'd find them. You just...find them. One is a game reference in big numbers on a folder, one is split in half and hid in two secret compartments (why), and the other is just on the floor. Considering how much time you spend reading about these people (Terry, Sam, and Oscar) there could've been a clever setup for the player to deduce the combination on their own. Maybe they didn't want the player to get stuck from experiencing the story or something.
The other is how drip fed the story and house are to the player/Katie. It feels like a haunted house or theme park attraction rather than a house where people lived. Everything leads to (double spoiler

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spoiler (click to show/hide)
the attic but to get here you run all around the house to find a key to unlock a door to find a combination to unlock a locker to find a hidden passage etc etc. When you get to the attic you learn that Sam wanted you to reach the attic in the first place.