There is an unspoken doctrine embedded in every modern bible version (NIV, NKJV, ESV, NASB, NLT, etc), and that doctrine is that God has not only failed to preserve his words perfectly, but that his words can be changed and is made subject to man's scholarship.
To date, the underlying text for modern bible versions is still "evolving." The Nestle-Aland text is a critical edition of the New Testament, and the source text of most modern Bible translations. Right now, it is already in its 28th edition.
That's why some Christians have complained that their 1984 NIV and their new 2011 NIV are so different as though the new 2011 NIV is another bible altogether. The reason is because they have removed a total of 32,863 words and added another 34,469 different words.
Source: NIV2011/NIV2010 Changes
That means that some of the words in their old 1984 NIV have "passed away" and were replaced by new and better ones so-called. I'll share a couple of examples here, one from the Old Testament, and one from the New Testament, so that we could see those differences for ourselves.
From the Old Testament:
Psalms 8:3-4 (NIV 1984) "When I consider your heavens, the work of your fingers, the moon and the stars, which you have set in place, what is man that you are mindful of him, the son of man that you care for him?"
Psalms 8:3-4 (NIV 2011) "When I consider your heavens, the work of your fingers, the moon and the stars, which you have set in place, what is mankind that you are mindful of them, human beings that you care for them?"
From the New Testament:
1 Corinthians 5:4-5 (NIV 1984) “When you are assembled in the name of our Lord Jesus and I am with you in spirit, and the power of our Lord Jesus is present, 5 hand this man over to Satan, so that the sinful nature may be destroyed and his spirit saved on the day of the Lord.”
1 Corinthians 5:4-5 (NIV 2011) “So when you are assembled and I am with you in spirit, and the power of our Lord Jesus is present, 5 hand this man over to Satan for the destruction of the flesh, so that his spirit may be saved on the day of the Lord.”
Are they the same? Is the NIV "faithful and true?" An honest and good heart (Luke 8:15) will admit the difference, and the wise in heart (Proverbs 16:21) will understand why the difference, and will depart from the evil.
Not many Christians might know this, that the Nestle-Aland text is actually under the supervision and control of the Roman Catholic Church (Vatican) through joint agreement with the United Bible Societies (UBS) which owns it. Therefore, every modern-day "bible" is a product of the Roman Catholic Church one way or another, so that every modern-day "Christian" is a Roman Catholic, one way or another.
Have you heard of the 1537 Matthews Bible or the 1560 Geneva?
Something you might find interesting is the 1993 Orthodox OT English translation. I have a copy but haven’t done a side by side comparison of the verses with the KJV. The reason I mention it is that it’s not a product of the Roman Catholic Church.