ANSWER:
1. Erasmus had knowledge of many manuscripts other than those he used for his first edition. Erasmus “began studying and collating NT MSS and observing thousands of variant readings in preparation for his own edition” (Eldon Jay Epp, “Decision Points in New Testament Textual Criticism,” Studies in The Theory and Method of New Testament Textual Criticism, edited by Epp and Gordon Fee, p. 18; quoting Bentley 1983: 35, 138). “It is well known also that Erasmus looked for manuscripts everywhere during his travels and that he borrowed them from everyone he could. Hence although the Textus Receptus was based mainly on the manuscripts which Erasmus found at Basel, it also included readings taken from others to which he had access. It agreed with the common faith because it was founded on manuscripts which in the providence of God were readily available” (Edward Hills, The King James Bible Defended, p. 198).
2. Erasmus knew about the variant readings that are known to modern textual critics.
a. As Frederick Nolan observed: “With respect to Manuscripts, it is indisputable that he [Erasmus] was acquainted with every variety which is known to us; HAVING DISTRIBUTED THEM INTO TWO PRINCIPAL CLASSES, one of which corresponds with the Complutensian edition [the Received Text], and the other with the Vatican manuscript [corresponding to the modern critical text]. And he has specified the positive grounds on which he received the one and rejected the other. The former was in the possession of the Greek church, the latter in that of the Latin; judging from the internal evidence he had as good reason to conclude the Eastern church had not corrupted their received text as he had grounds to suspect the Rhodians from whom the Western church derived their manuscripts, had accommodated them to the Latin Vulgate. One short insinuation which he has thrown out, sufficiently proves that his objections to these manuscripts lay more deep; and they do immortal credit to his sagacity. In the age in which the Vulgate was formed, the church, he was aware, was infested with Origenists and Arians; an affinity between any manuscript and that version, consequently conveyed some suspicion that its text was corrupted" (Nolan, Inquiry into the Integrity of the Greek Vulgate, or Received Text of the New Testament, London, 1815, pp. 413-15).
b. “For the first edition Erasmus had before him ten manuscripts, four of which he found in England, and five at Basle. ... The last codex was lent him by John Reuchlin ... (and) ‘appeared to Erasmus so old that it might have come from the apostolic age.’ He was aware of Vaticanus in the Vatican Library and had a friend by the name of Bombasius research that for him. He, however, rejected the characteristic variants of Vaticanus which distinguishes itself from the Received Text. (These variants are what would become the distinguishing characteristics of the critical text more than 350 years later.)” (Preserved Smith, Erasmus: A Study of His Life, Ideals, and Place in History, 1923). Erasmus was given 365 select readings from Vaticanus. “A correspondent of Erasmus in 1533 sent that scholar a number of selected readings from it [Codex B], as proof [or so says that correspondent] of its superiority to the Received Text” (Frederic Kenyon, Our Bible and the Ancient Manuscripts, 1895; S.P. Tregelles, On the Printed Text of the Greek Testament; cited from Hills).
c. Erasmus discussed these variants in his notes. “Indeed almost all the important variant readings known to scholars today were already known to Erasmus more than 460 years ago and discussed in the notes (previously prepared) which he placed after the text in his editions of the Greek New Testament. Here, for example, Erasmus dealt with such problem passages as the conclusion of the Lord’s Prayer (Matt. 6:13), the interview of the rich young man with Jesus (Matt. 19:17-22), the ending of Mark (Mark 16:9-20), the angelic song (Luke 2:14), the angel, agony, and bloody seat omitted (Luke 22:43-44), the woman taken in adultery (John 7:53-8:11), and the mystery of godliness” (1 Tim. 3:16) (Edward Hills, pp. 198-199).
3. Erasmus also had the textual evidence from the writings of ancient church leaders and from ancient Bible translations. “Nothing was more important at the dawn of the Reformation than the publication of the Testament of Jesus Christ in the original language. Never had Erasmus worked so carefully. ‘If I told what sweat it cost me, no one would believe me.’ HE HAD COLLATED MANY GREEK MSS. of the New Testament, and WAS SURROUNDED BY ALL THE COMMENTARIES AND TRANSLATIONS, by the writings of Origen, Cyprian, Ambrose, Basil, Chrysostom, Cyril, Jerome, and Augustine. ... When a knowledge of Hebrew was necessary, he had consulted Capito, and more particularly Ecolampadius. Nothing without Theseus, said he of the latter, making use of a Greek proverb” (J.H. Merle D’Aubigne, History of the Reformation of the Sixteenth Century, New York: Hurst & Company, 1835, Vol. 5, p. 157).
