You can if it’s in a treaty. Russia kept all the territory that it took from the Qing government as spoils of war. However, that does not apply to the Spratly Islands because prior to Japan claiming those islands, no one officially claimed the Spratly islands. This topic has been discussed in China's nine-dashed line (which is actually Taiwan's eleven-dashed line)
There is no treaty that recognized Chinese claims over the Spratly islands, just a maybe concede by the French on the Paracel islands on behalf of Vietnam.
However, the Japanese basically took over most of the atolls by the 1920s, and the French drove the Japanese away from the Spratly islands in 1933. Then WW2 happened, all the islands were under Japanese control, and most of them were placed under the administration of the Takao (Kaohsiung) City.
Basically only the Japanese and the French made actual claims on the Spratly Islands before the war.
Official post-war status is:
The KMT was instructed by General Order No. 1 to takeover Taiping Island from the Japanese, as a result, its international status is actually exactly the same as Taiwan, not to mention it was placed under the administration of Kaohsiung in the Japanese era. Technically it is a territory trusted to the Allied Powers, which operated under the rules of the UN post war.
Regardless,
Permanent Court of Arbitration in The Hague ruled back in 2016 that none of the “islands” in the South China Sea are actual islands, but just reefs, shoals, and atolls, they can’t be claimed as territories, and the EEZ can’t be allied to any of them.
So if international law was to be observed, the entire area is international waters. If we are to go by international law, it’s either that, or the Treaty of San Francisco, which would place the Spratly Islands under the administration of Taiwan.