In early 1949, a Draft Report by the US National Security Council determined that while Formosa and the Pescadores were under the de facto control of the Chinese Nationalists, these islands were still legally a portion of the Japanese Empire.
Draft Report: by the National Security Council
Date: January 19, 1949
Subject: U.S. policy with respect to Formosa and the Pescadores
3. The present legal status of Formosa and the Pescadores is that they are a portion of the Japanese Empire awaiting final disposition by a treaty of peace. The U.S. position regarding the status of the islands is qualified by the Cairo Declaration by the Chiefs of State of the U.S., U.K. and China and the policy which the U.S. has followed since V-J Day of facilitating and recognizing Chinese de facto control over the islands.
[ source: United States Department of State / Foreign relations of the United States, 1949. The Far East: China, Volume IX (1949), page 271 ]
See -- FRUS page for full content
[Chinese version] https://www.twdefense.info/trust3/frusch-1949av.htm