The Greek Textus Receptus underlying the KJV was first edited by Desiderius Erasmus and published in 1516. Erasmus had before him a half-dozen manuscripts during the editing process. Critics are quick to seize upon this "flaw" of the Textus Receptus to deride the KJV. However, these criticisms are unjustified.
There is a theological problem with deriding the Textus Receptus on the basis that its original edition descends from just a few manuscripts. Our theory of textual criticism must be based on what the Bible says about textual transmission, not on the philosophies of liberal theologians. The Bible is clear that God can use only a handful of manuscripts to preserve his words.
The Bible describes a time when Hilkiah the high priest found the "book of the law" (2 Kings 22:8) or the "book of the covenant" (2 Kings 23:2) in the house of the LORD during the reign of Josiah. The book of the law, whether it was just the five books of Moses or a collection of all the biblical books written up until that time, had to be rediscovered during Josiah's reign because the previous wicked generations under Manasseh and Amon had apparently eradicated the book of the law from the land. This eradication of the biblical books was so widespread that even the high priest did not possess them until he discovered them in the temple.
This book found by Hilkiah became the ancestral copy of all the Hebrew manuscripts that exist today. One could speculate that Hilkiah found other manuscripts in other places over time, but that would be a speculation since the Bible does not say so. The Bible clearly portrays this single copy found in the temple as the sole catalyst for the great spiritual revival during Josiah's time and the rediscovery of God's words for subsequent generations. Ezra, a direct descendant of Hilkiah (Ezra 7:1), canonized the Old Testament and transmitted it to future generations. Ezra's Old Testament was surely based on Hilkiah's copy found in the temple. The readings of this copy eventually diverged into the various Old Testament streams extant today, such as the Masoretic, Dead Sea Scrolls, Samaritan and LXX. Whether or not Hilkiah or Ezra found other manuscripts besides the one found in the temple during Josiah's reign, the Bible is clear that the number of manuscripts does not matter as long as God providentially provides the manuscripts for a time of spiritual revival. King Josiah saw the hand of God in preserving this single copy and never doubted its authenticity or integrity. He caused the words of this single copy to be read to the people (2 Kings 23:2).
There is a strong parallel between Hilkiah and Desiderius Erasmus, the originator of the Textus Receptus. Both were men of high repute and rank. Both were upright while their contemporaries were apostate. Both caused God's words to be published after a time of spiritual darkness. Both were catalysts of a great spiritual awakening. The Textus Receptus was to the Reformation what Hilkiah's discovery was to the revival in Josiah's days. Modern textual critics need to learn what the Bible says about textual transmission. If God wants his words to be published for a time of spiritual awakening, he can do so through even just one manuscript.
In any event, the fact that Erasmus had only a handful of manuscripts during his preparation of the 1516 edition is irrelevant in regards to the reliability of the text underlying the KJV. First of all, no scholar disputes the fact that Erasmus had studied variant readings of the New Testament throughout his life prior to publishing the Textus Receptus. In fact, the study of variant readings in the Greek New Testament did not begin with Erasmus but with scholars such as Thomas Linacre (1460-1524) and John Colet (1467-1519), and even as far back as Jerome (347-420). Although Erasmus spent only two years in front of a handful of Greek manuscripts to compose his first edition, his knowledge concerning the Greek New Testament and its variants did not come solely from looking at these few manuscripts in the two year period. Secondly, the KJV was completed in 1611 – almost a century after Erasmus composed his first edition of the Textus Receptus in 1516. The KJV translators most likely used the 1598 edition of Beza. At least three-quarters of a century of scholarship had gone into the Textus Receptus by the time of the KJV. Erasmus updated his Textus Receptus in 1519, 1522, and 1527. Stephanus also edited the Textus Receptus in 1546, 1549, 1550, and 1551. Beza edited the Textus Receptus nine times between 1565 and 1604.
Critics are quick to point out that Erasmus back-translated the last six verses of Revelation for his 1516 edition. But despite this charge, we see that Erasmus included a reading in Revelation 22:20 that exists in the Greek and not in any edition of the Vulgate (i.e. "αμην ναι ερχου (Amen. Even so, come)” instead of “amen veni (Amen. Come)"). This is one evidence that Erasmus was not confined to the readings contained in the few manuscripts placed before him during his editing of the 1516 edition. At the very least, Erasmus consulted notes such as the annotations of Laurentius Valla. The charge with respect to Erasmus' treatment of Revelation 22:16-21 is dealt with in on the website. The analysis shows that the only translatable differences between the Textus Receptus and other extant Greek manuscripts are two small words: καὶ and γὰρ.
As for the alleged "countless hundreds of printing errors" in Erasmus' first edition, these were corrected in later editions of the Textus Receptus by Erasmus himself and others, and never made their way into the KJV.
The KJV translators were not ignorant of the body of manuscripts and variant readings. The 1611 KJV has marginal notes next to the following verses showing alternate readings:
Matthew 1:11, Matthew 26:26, Luke 10:22, Luke 17:36, John 18:13, Acts 25:6, Ephesians 6:9, James 2:18, 1 Peter 2:21, Peter 2:2, 11, 18, 2 John 8.
This shows that the KJV translators were not translating in a Textus Receptus vacuum. There were other manuscripts available to the KJV translators, and yet they used the Textus Receptus.
Lastly, the majority of manuscripts that have been discovered and catalogued in the past four hundred years agree more with the Textus Receptus than with the modern Nestle-Aland/United Bible Society (NA/UBS) text. The majority of these manuscripts, termed the Byzantine Majority Text by scholars such as Wilbur Pickering, Zane C. Hodges, Maurice A. Robinson, are in the Byzantine tradition which generally agrees with the Textus Receptus. The Byzantine/Majority Text (2000) can be viewed at Biblos.com. While it is true that no extant Byzantine manuscript matches the Textus Receptus perfectly, the same could be said that no extant Alexandrian manuscript matches the NA/UBS text. The NA/UBS text is highly edited, being a composite text of readings from Codex Sinaiticus, Codex Vaticanus, and other manuscripts, all of which disagree with each other in thousands of places (John William Burgon, The Revision Revised, p. 11). With respect to the differences of whole verses, Codex Vaticanus does not have Matthew 12:47, forty-five chapters of Genesis, portions of Hebrews, the Pastoral Epistles, and Revelation. Codex Sinaiticus does not have Matthew 24:35, Luke 10:32, Luke 17:35, John 9:38, John 16:15, John 21:25, and 1 Corinthians 13:2. Papyri are just fragments of various books.