The fact that there was some prior recognition is quite irrelevant. Should the EU nations claim their pre 1911 boundaries against the will of the people living there, by force?
Should the Lenape Native Americans whose predecessors sold Manhattan to the Dutch be able to reclaim it by force? How about the Dutch?
Your argument is sophistry, and nothing but inane justification for an authoritarian and expansionist regime.
Moreover while that regime repeatedly proclaims that no one should interfere in the internal affairs of other nations, it feels completely free to interfere and claim other nations, including, Tibet, Taiwan, and Hong Kong (yes it was leased and returned, but they are already violating the terms of the return).
This is not a regime to defend.
This Chinese tone that "justifies" the invasion creates these kinds of side discussions, which serves the same purpose as Whataboutism, even if that isn't the intent of the speaker/writer.
A thought experiment: Assume that Tibet was actually some kind of horrific feudal empire that did whatever horrible things to its people you can imagine.
Even if that is some kind of justification for an invasion, e.g., the people had pleaded with the CCP to get freed - which they did not, it is CCP's actions ever since the invasion that betray's their intent.
If the goal had been to free the Tibetean people, they would have removed the leadership, which was done in days, and then freed the people. But CCP has done the opposite, consistently holding more tightly to the land, eliminating the Tibetian's culture and freedom, and claiming ownership.
It is as if the US had not only invaded Iraq to remove the dictator who annexed adjacent countries, but then claimed the land and oil as it's own, and also started systematically removing all mosques, moving US families into each town, and imposing American culture on Iraq.
China are illegitimate occupiers, and wrongfully claim stolen Tibetan territory as their own. Full Stop.