What does it mean to be righteous?
Actually, the WTS puts righteousness in context of the historical times or they say they do.
They point out there was no written law code against fornication, adultery, polygamy, incest (note that Lot's daughters were adults and they initiated the sexual contact with their father according to the story; this is not the case of an adult father sexually raping his minor children), etc.
Yet, they praise Joseph for not committing adultery although there was no written law code (for Abraham's descendants; they may have been written laws against adultery for the Egyptians) yet excused Judah for committing fornication with a temple prostitute (really his daughter-in-law Tamar) because there was no law code.
The WTS teaches there are ways to know right and wrong without a written law code by quoting:
For whenever people of the nations that do not have law do by nature the things of the law, these people, although not having law, are a law to themselves. 15
They are the very ones who demonstrate the matter of the law to be written in their hearts, while their conscience is bearing witness with them and, between their own thoughts, they are being accused or even excused.
So based on that scripture, did Joseph, Judah, or Lot need a written law code to know these things were 'wrong'? This is what the WTS reaps when they use OT examples to teach people how to be Christians.