[ithkuil]

Yes. In practice the cat, box, posion and Geiger counter system is not a fully closed system, and it gets entangled with the observer through unavoidable interactions.

When the observer's state gets entangled with the cat's state (whether gradually or suddenly) it's still perfectly valid to say that the cat is in a superposition of being dead and alive, and so is the observer in the superposition of observing the cat dead and observing the cat alive. That doesn't mean that the observer ever can nor should observe the cat being both dead and alive.