The Arthashastra, the ancient treatise on statecraft attributed to Kautilya, sets out how the king’s spies report to him. Reports reach the court through several separate lines of spies.
In R. Shamasastry’s translation: “When the information thus received from these three different sources is exactly of the same version, it shall be held reliable. If they (the three sources) frequently differ, the spies concerned shall either be punished in secret or dismissed.”