Note: Before dad 2 you also can walk around the trigger but at some point you gotta go get the other plates

Another interesting thing is that if you cheat to give yourself one plate, the cutscenes are offset by one plate.

Which tells us that the game uses some other flag to infer that you have completed a plate sequence

If I have to guess it's the same flag that tells game that a realm has been "completed" and thus prevents the end from loading when you enter a second time.