Earlier quoted context omitted.
This is indeed a problem, but doesn't appear to be the issue in this case. In a sense, this is the opposite. It's more like: The law says: pressure vessels must be pretty sturdy even when really hot. A standard comes along and proclaims to abide by said law, while fleshing out the details of how sturdy and how hot. Lawyers and judges then make reference to it as what the law always meant, and effectively give it lega…
There should be a difference. If I show my pressure vessel fits the standard the court can accept that under the assumption that the standard is good. Or I can go back to first principals of engineering and show the court that my vessel is correct.
There isn't always a "correct" in any way you can prove. Often you just have norms.
If someone heats the vessel up to an arbitrary temperature X, and it explodes, yet the standard which everyone except you followed said it must withstand arbitrary temperature Y, then the court may be inclined to ignore your arguments that temperature X was good enough.
Rather than being something you can derive from nature, laws and standards often contain arbitrary values which take into account margins for human error or other "reasonable" measures.
In this way, norms gain legal power.