The faction name is beyond my capacity to change; It should in fact be "Âpârnîg" or "Pârnîg". Back in 272 BCE there was no such thing as an Arsacid dynasty; It had to first be established by the one Arsaces who toppled Andragoras/Pherecles and dubbed himself Arsaces I. However it was the Arsacids who gave rise to the legend of the "champion horse-men", or "Pahlavân"; Their succession in Parthia proper, or Parthava, caused a transition in the nomenclature of the area. Parthava became Pahlava. It is the idea that counts.

Yeah, migraine-inducing when you give a serious moment of thought. Today's terminology is fucked up thanks to a bunch of senile folks who want everything to be simplified for them (When it usually needs a correct abstraction).