OK, I may have founf the answer. The aa gun converts ownership to the new owner of the territory, whoever that is. So, because the British will own the territory, they will own the aa gun.
So, in theory, the chinese could own an aa gun with Russian help. If the Russians captured a Japanese aa gun in Manchuria, the aa gun would go over to the Chinese as owners of the liberated territory.
Also, you might have a strange scenerio where the India aa gun is taken to the Phillippenes by the Japanese after it is captured. Then the Phillipenes is liberated by the Soviets (I know its very unlikley). So, a British aa gun, on US territory, liberated by the Soviets…. it would be a US aa gun as they are the new owners of the freshly liberated territory.
Can you confirm that this is correct Krieghund?