The Societas Rosicruciana in Anglia is not open. Membership requires that a man already be a Master Mason in good standing and a Trinitarian Christian, and admission is by invitation. That makes it a study body inside Freemasonry rather than a rival to it, and it explains why its papers read like a scholarly society's transactions: members research and present, and the grades mark study rather than initiation into a practice.
The structure is nine grades in three orders, following the pattern of the eighteenth century German Gold und Rosenkreuz, and it is that ladder, more than any doctrine, which the Golden Dawn took. Westcott, Woodman and Mathers were all members here first. When they built an order that admitted women and non-Masons and taught practical magic, they were opening a closed structure rather than inventing one.
Robert Wentworth Little said he had found the founding documents among papers at Freemasons' Hall. That account has been questioned since, and it belongs to a recognisable pattern in this period, in which a new body authenticates itself with a discovered manuscript or a foreign correspondent. The Golden Dawn did the same thing twenty years later with the cipher manuscripts and Anna Sprengel. Reading the two claims side by side is more instructive than assessing either alone.