The Secret Chiefs, the governing authority the Golden Dawn's own teaching assigns to its Third Order, are themselves a publicly documented concept: general histories of the order describe the claim, recorded in Israel Regardie's published editions of the order's papers, that Ipsissimus and its two companion grades were understood as administered by this authority rather than by the order's ordinary Second Order structure.
Published scholarship on the Golden Dawn treats the Third Order as more a stated ideal within the grade structure than a tier the historical order regularly conferred, a point general accounts make explicitly when discussing how few members, if any, were formally recognized at this level through the original order's own administration.
Because the A A later adapted the same grade name and number for its own highest tier, general reference works on both orders discuss Ipsissimus as a point of direct published continuity between Crowley's system and the order he had left, distinguishing what the two organizations share from where their published teachings diverge.
General histories of the Golden Dawn treat the Secret Chiefs concept itself as one of the order's most discussed published ideas, cited repeatedly in later scholarship on both the Golden Dawn and the occult revival more broadly as a template for how a ceremonial order can claim authority beyond its own visible officers.