The following law journal articles and other references fully show that Oct. 25 1945, was the beginning of the military occupation of Taiwan. In other words, there was no "Taiwan Retrocession Day."

Resolving Cross-Strait Relations Between China and Taiwan
http://www.taiwanbasic.com/lawjrn/res-cs1.htm

Historical and Legal Aspects of the International Status of Taiwan (Formosa)
http://www.taiwanbasic.com/lawjrn/historical-legal2b.htm

Who Owns Taiwan: A Search for International Title
http://www.taiwanbasic.com/lawjrn/who_owns_tai3.htm

UK Parliament
http://www.taiwanbasic.com/hansard/uk/uk1955as.htm

Congressional Research Service
http://www.taiwanbasic.com/congress/crs-sinojapan.htm

Foreign Relations of the United States
http://www.taiwanbasic.com/state/frus/taiwan/frus1946aq.htm

CIA Report
http://www.twinfopost.com/excerpt21.htm

* the occupation of territory in wartime is essentially a temporary, de facto situation, which deprives the occupied Power of neither its statehood nor its sovereignty; it merely interferes with its power to exercise its rights.

* while a situation of occupation may in fact prevent a government from exercising sovereignty over part or all of its territory, this does not confer sovereign rights on the occupant. Occupation is by definition a temporary situation that interferes with, but does not diminish or terminate, the sovereign rights of the people under occupation.


REFERENCE: http://www.icrc.org/ihl/COM/380-600054?OpenDocument

Three Questions

In relation to the military occupation of a particular area, we are faced with three central questions, (which all must be answered based on the customary laws of warfare):

1. When does the military occupation begin?
2. Who is "the occupying power"?
3. When did the military occupation end?

In order to sort out the answers to these questions, we have to do a thorough overview the customary laws regarding military occupation.

In the Hague Regulations, we can look at SECTION III: MILITARY AUTHORITY OVER THE TERRITORY OF THE HOSTILE STATE

Art. 42.   Territory is considered occupied when it is actually placed under the authority of the hostile army. The occupation extends only to the territory where such authority has been established and can be exercised.

This HR 42 is quoted in US Army Field Manual, FM 27-10, The Law of Land Warfare, para. 351, as being the definition of "military occupation," as well as being some sort of gauge for marking the point in time when the military occupation begins.