Matsyendranath survives only in Nath and Kaula tradition and in Newar devotional practice, and different lineages and modern scholars place him across several centuries with no external, independently datable evidence to settle the question.
What would resolve this An inscription, manuscript colophon or external record independently naming Matsyendranath and a date, distinct from the devotional and lineage traditions that presently supply the only accounts of his life.
OpenHistory of tantra and hatha yoga, Nath Sampradaya studies, Newar religious historyDavid Gordon White, The Alchemical Body: Siddha Traditions in Medieval India