Even if it was tested by the courts, you can appeal. And even after the appeal, you can appeal to a higher court, all the way to the Supreme. And even if was tested there, congress can pass a law that allows it. And even if that happens the Supreme court can strike down the law. And even if that happens, the public can mount a revolution and tear down the legal system.
But, practically speaking, Opus has extremely good guarantees for being unencumbered, as much as is possible - the people working on it have given licenses to use it, and experts in the field have had a while to go over this stuff. Nothing is 100%, but this is as good as it gets.