pre-Galfridian
According to Wikipedia’s article on King Arthur:
“The familiar literary persona of Arthur began with Geoffrey of Monmouth’s pseudo-historical Historia Regum Britanniae (History of the Kings of Britain), written in the 1130s. The textual sources for [the legend of] Arthur are usually divided into those written before Geoffrey's Historia (known as pre-Galfridian texts, from the Latin form of Geoffrey, Galfridus) and those written afterwards, which could not avoid his influence (Galfridian, or post-Galfridian, texts).”
I’m finding it difficult to avoid misreading Galfridian as Gallifreyan.