Suffice it to say we have better tools, methods and knowledge regarding translations of ancient Greek than they did back then. And they did not translate the original KJV Bible from scratch, but rather from another translation of the Bible.
The KJV was translated using over 5000 different sources in Hebrew, Greek and Latin; collectively known as the Textus Receptus. In the 1800s two new versions of the New Testament were discovered, written in Coptic Egyptian and known as the Alexandrian Codices. They dated back further than the texts in the Textus Receptus and so were believed to be more accurate. They vary wildly from the Textus Receptus, even omitting entire verses and are what most modern English translations (including the NIV) are based on.
HOWEVER, in the time since there have been over 24,000 fragments and complete texts of the New Testament discovered. Many of which are older than the Alexandrian Codices. They’ve been assembled together collectively as The Majority Text. With all 24,000 pieces available for comparison, they agree over 90% with the original Textus Receptus. The basis of the King James Bible.
And if by “doctrine” you’re referring to the '11 NIV including “brothers and sisters” in places, my understanding is that the wording used in the original source text was considered more gender-neutral back then than to deliberately address only just men.
By doctrine I mean the myriad examples listed in that second link in my post.