Following the Circular 183/2011/TT-BTC:
Article 2, Clause 10: Valuation date is the date when fund determines the NAV.
Article 2 Clause 11: Trading date (T date) is the valuation date (Article 2 Clause 11 Circular 183/2011/TT-BTC).
Article 19 Clause 1: Net Asset Value (NAV) means the total asset value owned by the Fund subtracts its related liabilities at the date prior to the valuation date.
NAV (per unit) used for trading date is the NAV at the date prior to the trading date.