The KJV was based on the received text ( Textus receptus) and that was based on the Majorial texts at the time and it was argued already that older manuscripts were available and not used.
The oldest texts we have today that can give us as complete a bibel as we can are the Codexes Sinaiticus and Vaticanus, both of which were found AFTER the KJV.
Modern translations have taken these and many other manuscripts into account and made "changes" accordingly.
As for the WBTS not stating who writes their articles or any of their publications:
While humility is a beautiful thing, there is a fine line between being humble ( or the pretense there of) and unqualified.