you don't make sense, Japan had the stronger claim before the purchase and it is only stronger now,<quoted text>
I can sell property in the UK that I have title deeds for to the French but simply because they would now own property in the UK would not grant the French sovereignty over it because the sovereignty would still remain with the English Crown. Only nations can transfer sovereignty between themselves, Individuals do not have that power.
If you think it is ironclad then you are grossly misjudging the Chinese resolve.
recent Chinese attempts to take the territory of other countries is just making people more resentful of China, especially neighboring countries