Historical evidence affirming Vietnam's sovereignty over the Hoang Sa and Truong Sa archipelago

Vietnam's sovereignty over the Hoang Sa and Truong Sa archipelagos was inherited from the Champa period, officially established from the Nguyen Lords, continuously through the Tay Son and Nguyen dynasties and up to the present. However, to have a correct understanding of sovereignty, there must be specific, correct historical evidence and a legal basis appropriate to each historical period, especially in the 17th-18th centuries, when there were no international conventions on sovereignty over seas and islands.