That advancement to the Societas Rosicruciana in Anglia's Third Order, Grades VIII and IX, rests solely with the society's Supreme Magus is documented openly in general Masonic reference works on the society's governance, a structural fact about Magus's own rank that is public information even where the society's ceremonial content is not.
Published histories of the SRIA and the Golden Dawn both note that the Golden Dawn's later Third Order, framed around the Secret Chiefs rather than a single named administering officer, diverges from the SRIA's Supreme Magus model even while sharing its numbered position at the top of a nine grade sequence, a documented point of structural difference between the two orders' highest tiers.
General reference works on the SRIA describe its Third Order as considerably smaller in practice than the First and Second, consistent with a single officer, rather than a body of Colleges or Provinces, controlling access to Magus and the grade beside it.
Because the society's Third Order caps at two grades, Magister and Magus, rather than the three the Golden Dawn later assigned its own Third Order, general comparative accounts treat this as one of the clearer documented structural differences between the two societies despite their shared lineage.