$$\require{cancel}$$
There is a fairly strong proof that only minimal physical assumptions (locality, causality) that the product of $$C$$, $$P$$ and $$T$$ is a good symmetry of any theory. Up to now experiment has not shown any breaking of this product. We would have to rethink a lot of basic physics if this symmetry is not present. I am reasonably confident that if breaking is ever found there will be ten models that can describe it within a month!