Yarsani adherents are folded into Iran's broader Muslim population in its national census, and no other government or denominational body maintains a count of them; every published figure is an undated snapshot from fieldwork, advocacy or journalism rather than one point in a tracked series.
What would resolve this A dedicated demographic study, most plausibly built from community register data the Yarsani community itself might keep informally, or from a specially commissioned survey, giving dated counts that could be compared over time the way this axis compares other bodies.
OpenDemography, Iranian religious minority studiesPhilip G. Kreyenbroek, The Religious Textual Heritage of the Yarsan (Ahl-e Haqq)