Okay, fair question. The Balfour Declaration was superseded by the MacDonald White Paper of 1939, which declared that the increased Jewish presence in Palestine demonstrated that the Declaration had been fulfilled. Henceforth Jewish immigration would be limited & land sales essentially curtailed. It also proposed a Palestinian-majority state with a "participating" Jewish minority.

Because the British turned over Palestine's future to the UN in 1947, none of those declarations or papers held any authority henceforth.