The shortest explanation: concretization is not an absolute; a KS test only reveals what the data allows to reveal.
If the input data are biased or incomplete, the test only concretizes a distorted reality.
The parsimony here is that validity depends directly on the quality of the underlying hypotheses.
For example, if reference data do not cover extreme stress regimes, the KS test cannot concretize the robustness of a reserves portfolio against a major liquidity crisis.