I mean law and accounting usually have a “right” answer that you can verify against. I can see a test data set being built for most professions. I’m sure open source helps with programming data but I doubt that’s even the majority of their training. If you have a company like Google you could collect data on decades of software work in all its dimensions from your workforce

It's not about invalidating your conclusion, but I'm not so sure about law having a right answer. At a very basic level, like hypothetical conduct used in basic legal training matrerials or MCQs, or in criminal/civil code based situations in well-abstracting Roman law-based jurisdictions, definitely. But the actual work, at least for most lawyers is to build on many layers of such abstractions to support your/client's viwepoint. And that level is already about persuasion of other people, not having the "right" legal argument or applying the most correct case found. And this part is not documented well, approaches changes a lot, even if law remains the same. Think of family law or law of succession - does not change much over centuries but every day, worldwide, millions of people spend huge amounts of money and energy on finding novel ways to turn those same paragraphs to their advantage and put their "loved" ones and relatives in a worse position.