Middle-Aged Rosicrucians?

Given that we know Emma wrote her own copy -- or William did for her -- things like this given me heartburn.

Granted that we have no evidence that Emma was any more familiar with Rosicrucian thinking than Hargrave Jennings' work could make her (now that we know she and Jennings were at Covent Garden together, that link feels secure), in what sense would a body of thought that dates from the Fama Fraternitatis in 1607, supposedly detailing the life of a man born no earlier than the year of the Great Schism be considered a document of the Middle Ages?