He has a valid point and does have legal implications. It is as serious as Republic of Austria made
to ban the return of Hubsburg family to Austria because the last emperor did not relinquish his claim to the sovereignty. Remember the complaints from western countries about the comments from Chinese ambassdor who said that Russian-Ukrainian border was never legally settled? It is a matter as serious as that.
Another example is PRC denounced multiple times ROC's constitutional amendment including abolishing Fujian and Taiwan province under ROC control. The ground is that ROC is legally bound to amend its constitution with representitives from populations in all its founding territory which includes mainland. PRC being sensitive to the matter is not because it cares much inside Taiwan, but PRC can not allow ROC to legally anounce independence without giving mainland the legal ground to attack it. Very often letters on paper matters.
