ISO 3166 is the international standard which records the official names of countries and territories. The official name of Taiwan Island per that standard is "Taiwan, Province of China".

As for "de facto independence", statehood works off of international recognition, not necessarily just the situation on the ground. Much of Palestine has been de facto occupied and integrated into Israel for just as long, yet very few people here (or internationally) recognize those occupied territories to be a legitimate part of Israel.