I just want to add my small slice of fanon here - because the Encyclopedia Eorzea contains information that by all rights should be extremely exclusive knowledge (the existence of the primal Phoenix, the true origin of the Void, etc.) but is also a towering work of scholarship that must have taken an immense amount of time to compile, there can really only be one author - Rammbroes Zasertylsyn, who as a founding member of the Circle of Knowing would be party to such secrets but as now a member of the Sons of Saint Coinach would have the time to actually write it all up.

The book was probably meant for publication exclusively within Sharlayan, copies were not meant to make their way to Eorzea itself.