Reports that the Yazidis possessed two secret books, a Book of Revelation spoken in the voice of the Peacock Angel and a Black Book of origins and observances, circulated among travellers and missionaries through the nineteenth century, and the demand created a supply. Around the turn of the twentieth century, manuscripts answering the description surfaced in northern Mesopotamia and were sold, through intermediaries including local Christian scribes, to European collectors and institutions; several were written in an otherwise unattested cipher script, presented as the Yazidis' secret alphabet. Scholarly publication followed quickly, most influentially in 1911 and 1913, and the texts entered the reference literature as the scriptures of the Yazidis.
Doubts kept pace. The cipher looked contrived, the copies multiplied suspiciously, and the Kurdish of the texts showed signs of composition by writers whose first language it was not. The position that consolidated across the twentieth century, and which the standard modern studies of Yazidism state plainly, is that the manuscripts sold to the West were products of the manuscript trade, written out by non-Yazidi scribes to meet collectors' expectations of what a secret scripture should be. The same scholarship adds the crucial counterweight: whoever wrote them knew Yazidi tradition well, for the cosmogony, the taboos and the festival calendar they describe correspond substantially to what the community's own oral corpus teaches.