Earlier quoted context omitted.
By that argument the UK could re annex parts of France and the USA. And Italy could take back large chunks of the near east.
Conversely, if not for that argument, China would be a hodgepodge of local warlords (what it was post Qing, before ROC's unification). A problem of claims by irredentism is what time period do you consider the proper extent of a nation's territory? This applies to both the rationalisation of Tibet belonging to China, and for not belonging.
If you can't force the issue (i.e Yugoslavia, Kosovo, Cyprus, Crimea) via a force of arms or diplomacy.