Q: The US Executive Branch has consistently maintained that Taiwan's status is undetermined. Now, however, since the Taiwan Civil Government (TCG) has presented abundant evidence to show that Taiwan as an overseas territory of the USA, doesn't this mean that Taiwan's status is already determined?

A: This is a common source of confusion. First, we have to clarify what we mean by "undetermined status" in this context. What this means is that Taiwan has not reached a final political status.

What is important to recognize is that as an overseas territory of, or (more colloquially) as an "insular area of" the United States of America, under the continued benign dominion of the United States Military Government, Taiwan has not yet reached a final political status.

So, to be very technical, we may ask the questions:
From a legal standpoint, is Taiwan a PART OF the United States???
The answer is NO.

Is Taiwan an independent sovereign nation?
The answer is NO.

Taiwan's legal status must be understood according to the provisions of the peace treaty. The correct interpretation of a treaty clause such as Article 2(b) in the San Francisco Peace Treaty
Japan renounces all right, title and claim to Formosa and the Pescadores.
where no "receiving country" is specified, is to say that Taiwan escheats to "the principal occupying power" (which is "the conqueror") as an interim status condition. This is not ownership, but rather a quasi-trusteeship.

So, this means that Taiwan is a quasi-trusteeship under military government within the US insular law framework.

Taiwan's final political status remains as undetermined.

Additional Webpages of Interest

Three Dates

Democratic Elections in Taiwan

Application of the Constitution's Bill of Rights