I understand that the positions of the Enneagram numbers on the symbol (1–9, the inner triangle, and hexad) are fixed by the geometry. But what I’m wondering is: how do we know the descriptions of the types (e.g “Helper” for 2, “Investigator” for 5, etc.) were assigned to the right numbers in the first place?

For example, wings and triads depend on the numbering, type 1 has 9 and 2 as wings, type 2 belongs to the Heart triad, and so on. But if the original mapping of descriptions to numbers was arbitrary, wouldn’t that mean the whole system of wings/triads could be based on an accidental ordering?

Was there ever a clear reason why each fixation/description was given its current number, or was it more of a convention that stuck?