"There are no more than 17 people on the island", yet the characters in the Meta-World keep increasing, despite Rokkenjima being cut off from the rest of the world.
Actually, it isn't. Because Kinzo, in his eccentricity, had a subway system installed under the island! And because it's
beneath the island, it completely avoids the red while providing the mastermind a means to bring in their minions to attack the unsuspecting conference attendees (I'm going to assume he spent enough to reach at least one other island in the Izu archipelago)
And since Kinzo being dead brought down the current number of people on the island, somebody from the conference initiates the first twilight, the persons from the subway sneak onto the island and perform the killings, burying the respective stakes into their victims. Then, on the tenth twilight, the survivors are abducted and taken from the island, possibly to be killed.
And the answer to the last riddle of Alliance of the Golden Witch?
What first made me curious was that there was a folder containing background pictures for the jail cells and the path to the Kuwadorian that is called "subway" (we could argue it means the other kind, which is a short tunnel for people to walk through, but that's just arguing semantics and this isn't in red) I inquired about it a long time ago, but it didn't get addressed and I didn't have a theory, so here you are then.