Eleven rookie pirates who happened to arrive at the same island in the same year — a numbered set produced by a threshold rather than by a choice.
Filed by its count, not its title
Reduced as a phrase, “The Eleven Supernovas” would sit on The Telling — but that would be reducing wording this reference chose. The set is filed under 11 · The Signal instead, because 11 is what its author chose, and a chosen number outranks an imposed one.
Eleven newly arrived pirates, grouped because each carried a bounty over one hundred million and each reached the same archipelago at the same moment. Nobody selected them and they are not a team; the number is a census.
An awkward number is the point. Four and seven feel designed, and a reader treats a designed set as a checklist the author has promised to complete. Eleven feels counted — the natural consequence of a threshold applied to whoever happened to qualify — and so the story is free to develop three of them fully and leave the rest as weather.
It is also the most efficient rival-introduction the medium has produced. Eleven contemporaries established in a handful of chapters gives a protagonist a generation to be measured against for the next twenty years of serialisation, at almost no narrative cost.
Eleven is a master number in the system this reference uses, and master numbers are never reduced. That fits a set defined by arriving early and being ignored — but the fit is a coincidence, and the arithmetic here has no more claim on Oda than the calendar does.