The pilum is securely attested by the late Roman Republic, but its origin is not: proposed sources range from the Samnites to the Iberian peninsula to independent Roman development, separated by centuries, and no single dated origin is established in the literature consulted.
What would resolve this Dated archaeological finds of proto-pilum weapons from the proposed source cultures, or a textual source describing its adoption that predates the surviving accounts.
OpenHistory of ancient weapons and technologyWikipedia: Pilum