The King James Version of the New Testament was based upon a Greek text (the Textus Receptus) that was marred by mistakes, containing the accumulated errors of fourteen centuries of manuscript copying. It was essentially the Greek text of the New Testament as edited by Beza, 1589, who closely followed that published by Erasmus, 1516-1535, which was based upon a few medieval manuscripts. The earliest and best of the eight manuscripts which Erasmus consulted was from the tenth century, and yet he made the least use of it because it differed most from the commonly received text; Beza had access to two manuscripts of great value, dating from the fifth and sixth centuries, but he made very little use of them because they differed from the text published by Erasmus. We now possess many more ancient manuscripts (about 9000 compared to just 10) of the New Testament, and thanks to another 400 years of biblical scholarship, are far better equipped to seek to recover the original wording of the Greek text. Much as we might love the KJV and the majesty of it’s Jacobean English, modern translations are more accurate.
If only that was true, if you look you will find there are only 2 streams of Bible versions, the true text of the Textus Receptus (Majority Text) on which the King James Version is based, and those which picked up the Alexandrian manuscripts (Minority Text) which have been shown to have deleted and changed many parts of the text and are unreliable. The Textus Receptus or Majority Text in which we find the vast majority of copies, has been attacked with changes, amendments, deletions, and what can only be seen attempts to diminish Gods truth. Many of the new modern versions such as the NIV and others are based on a few corrupted manuscripts which form the basis of the Minority Text, many which can be traced back to their original source, the Alexandrian codices.
From what I have come across it seems that the Majority Text (Textus Receptus), also called the Byzantine Text is based on the vast majority of manuscripts still in existence. The manuscripts were brought together by many were faithful to its text such as Lucian, Erasmus, Stephanus, Beza and the Elzevir brothers to form the text known as Textus Receptus. When the Protestant Reformers decided to translate the scriptures directly from Greek into the languages of Europe, they selected Textus Receptus as their foundation Greek document and for good reason.
Here is a good description of how the corruptions were weighed and found wanting, in the book LET'S WEIGH THE EVIDENCE by Barry Burton which gives a easy to understand explanation...
"...There Are Two Kinds of Manuscripts:
Accurate Copies
These manuscripts represent the manuscripts from which the "
Textus Receptus" or Received Text was taken.
They are the majority of Greek manuscripts which agree with each other and have been accepted by Bible believing Christians down through the centuries. It is from these manuscripts that the King James Bible was translated in 1611.
Corrupted Copies
These manuscripts represent the corrupted copies of the Bible, also known as the Alexandrian manuscripts. These manuscripts, many times, do not even agree with each other. The Vaticanus and Sinaiticus manuscripts are part of this group. These are the manuscripts on which Westcott and Hort and the modern versions rely so heavily.
There are 5,309 surviving Greek manuscripts that contain all or part of the New Testament. These manuscripts agree together 95% of the time. The other 5% account for the differences between the King James and the modern versions.
The modern versions had to use the Textus Receptus, since it contains the majority of the surviving Greek manuscripts. The problem is that, when the Textus Receptus disagreed with the Alexandrian manuscripts, such as the Vaticanus or the Sinaiticus, they preferred these corrupted manuscripts over the Textus Receptus the Majority Text."
"..The Minority Texts were rejected by the early Christians and also by all the Protestant Reformers of the 15th, 16th and 17th centuries. The Reformers, who were well aware of the existence of
the Minority Texts, considered them unfit for translation purposes.
It is believed that the Minority Texts were butchered by Egyptian gnosticism with many changes, which are mostly deletions. The gnostics were a group that did not believe:
In the virgin birth, that Jesus was the Son of God, that Jesus was resurrected to heaven, that Jesus was the Creator, or that Jesus made atonement for our sins. There are many alterations in the Minority Texts, often a single manuscript being amended by several different scribes over a period of many years.
The Minority Texts omit approximately 200 versus from the Scriptures. This is equivalent to omitting First and Second Peter. The Minority Texts contradict themselves in hundreds of places...."
http://endtimeoutreach.com/whichbible.html
Here is some more background on the corruption of the Minority Text from another site....
"...almost all modern English bibles translated since 1898 are based on the Minority Text (this includes the New American Standard Bible, the New International Version, the Living Bible, the New Revised Standard Version, the New World Translation, the New Century Version, the Good News Bible, etc.). These bible versions are only supported by about five of the over 5,000 manuscripts in existence, or about .1% of all manuscripts, which is why it's also known as the "Minority text.".
The two most prominent manuscripts of the Minority Texts are the Vaticanus and the Sinaiticus....These Minority Texts frequently disagreed with each other as well as with the Majority Text, and also contained many obvious and flagrant mistakes. Up until the late 1800s, the Minority Texts were utterly rejected by Christians.
The fact that these two manuscripts may have been older does not prove they are better. More likely it indicates that they were set aside because of their numerous errors....
The Vaticanus, which is the sole property of the Roman Catholic Church, and the Sinaiticus, are both known to be overwhelmed with errors. Words and whole phrases are repeated twice in succession or completely omitted, while the entire manuscript has had the text mutilated by some person or persons who ran over every letter with a pen making exact identification of many of the characters impossible...."
"...One of the manuscripts that make up the Minority Text is the Vaticanus. The Vaticanus was found in 1481 in the Vatican library. The other manuscript is the Sinaiticus. The Sinaiticus was found in 1844 in a trash pile at Saint Catherine's monastery, and rescued from a long (and well-deserved) obscurity. It has a great number of omissions and has many words and phrases marked out and re-written. Both of these manuscripts are from Roman Catholic origin...."
http://www.ecclesia.org/truth/nt_manuscripts.html