Magic lore question: inconsistancy?

[Enkidoh]

Also it should be noted that it was stated that magic as it's known now has only been known and practiced for a comparatively short amount of time. Before then, there were other schools of magic taught which fell out of use as time went by and the newer schools of magic were developed. When you first join the CNJ's Guild the receptionist actually states this:

"Primitive magic such as that once wrought by individuals known as mages - meaning those with the ability to manipulate aether - has existed since the dawn of time."
"It was not until some five centuries ago that conjury emerged from this shapeless agglomeration of spells and charms - an event that led to the founding of Gridania."

Really, the three predominate 'legal' magical disciplines found in Eorzea - Conjury, Thaumaturguy and Arcanima - have only really come about in the last century or so and were developed from earlier magical techniques.