The NIV (and the NASB to a degree) have redacted New Testaments, because they used corrupted manuscripts. This goes back to the 3rd century, when people were already taking offense to the gospels and other NT passages, and changing them to their liking.
The manuscripts used for many modern translations were assembled in the late 19th century by a couple of "intellectuals," but the Textus Receptus/Majority Text were put together by Desiderius Erasmus in the late 16th century. The TR/MT are used by the King James translation.
All the manuscripts have mistakes—if they had one that they could be sure had every letter exactly as it was first written by the author of that book they would use it, but each surviving manuscript is the product of repeated recopying and the copyists inevitably made mistakes in their work. The same problem exists for the texts of all the other ancient authors—Homer, Plato, Cicero, etc. The editors do the best they can to restore the original text but at times they cannot be sure how the text originally read.