In regard to the cancellation or abrogation of the Treaty of Shimonoseki, China made several unilaterall announcements about this in the late 1930’s and early 1940’s. All of those are invalid.
The correct interpretation is that according to Article 4 of the Chinese-Japanese Peace Treaty (which came into effect on August 5, 1952), all treaties (concluded before 1941) between China and Japan are “terminated” because the war has come to an end.
In other words, any statements by the Chinese that any such treaties were “terminated” before this date are invalid.
However, it is important to remember that what can be “terminated” or “cancelled” are merely those provisions of a treaty which have continuing validity at the time of the “cancellation.” In order to return to the so-called “original status”, with Taiwan under full Chinese administrative authority, would require the negotiation of a new treaty with specific provisions to that effect.
In fact, Japan renounced all right, claim, and title to “Formosa and the Pescadores” in the San Francisco Peace Treaty (which came into effect on April 28, 1952), and reiterated this statement in the Chinese-Japanese Peace Treaty. However, these areas were not given to the Republic of China.
See Treaty of Shimonoseki
isop.ucla.edu/eas/documents/ … treaty.htm