This has nothing to do with political issue but, in my geological viewpoint as an islander in the Pacific, I think we should imagine why people did not live in those small islands of Spratley for centuries to claim dominium.
Ocean current, typhoon, earthquake and tsunami could have not allowed people and artificial structure keep staying on the coral sand for long time. Logistics is also fatal. Even aggressive IJA/IJN did not take such risk.
One big 'natural' explosion on the seabed nearby would solve the problem after all.