The page says any intelligent system faces exactly three problems, and that this is a mathematical necessity.
Then it defines the subject as something that models the world, picks actions for goals, spends a budget over time, and lives among other agents.
Those four jobs are the three problems: modeling-plus-acting is World, the budget is Time, the other agents are Self. "Exactly three" follows from how the subject was written. It does not follow from ruling out a fourth candidate.
A simple reinforcement-learning agent is said to satisfy the definition. A lonely chess engine models, acts, and discounts. It does not have a Self problem unless you put other agents in the room. The fourth clause of the definition and the specimen list are not the same subject.
Then drop the lonely agent. Keep the three problems for systems that actually share a room.
What's still open is the insect. An insect navigating is offered as the same subject as a civilization. If Self only starts when there are other agents, the insect needs a colony or it does not belong on that list. I'm not asking anyone to score bees. The specimen list is doing extra work the definition does not support.
The other reading: Self also covers "sub-modules within a single mind," so a lonely agent still has a boundary problem among its parts.
Then the insect still has to have parts that could optimize for themselves. The page never shows that. I don't know whether Self is a many-body problem or an inside-the-agent one. Those are different geometries. Stopping there rather than inventing a scoring rule for organs.