Rather than my trying to explain it again, I believe it is best to let the quotes of others tell what I have been trying to express.
Please keep in mind that these are not KJV-only sources, either.
GotQuestions.org:
"Codex Sinaiticus, also known as 'Aleph' (the Hebrew letter א)... has been highly valued by Bible scholars in their efforts to reconstruct the original biblical text. Sinaiticus has heavily influenced the translation work of modern Bible versions... Codex Vaticanus, also known as 'B'... is one of the oldest and most complete Greek Bibles. It was first used as a source document by Erasmus... It has been instrumental in constructing a critical Greek text, which is the basis for many modern Bible translations."
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GotQuestions.org)
The Text of the Gospels Blog:
"NA most definitely is an eclectic text; it is eclectically drawn from the texts of B and Aleph... Readings found in as many as 3000 other manuscripts are routinely ignored whenever they differ from the united testimony of B and Aleph."
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The Text of the Gospels)
Wikipedia:
"Codex Vaticanus (B) and Codex Sinaiticus (ℵ) are considered two of the most important manuscripts for establishing the text of the New Testament. They are key witnesses to the Alexandrian text-type and have heavily influenced modern critical editions of the Greek New Testament, such as the Nestle-Aland Novum Testamentum Graece."
Link to source (
Wikipedia)
Theopedia:
"The Codex Vaticanus and Codex Sinaiticus are the two most important manuscripts for the reconstruction of the original New Testament text. They are frequently referenced in modern critical editions like the Nestle-Aland 28, where their readings often serve as the basis for determining the original text."
Biblical Archaeology Society:
"Codex Vaticanus and Codex Sinaiticus are among the oldest and most significant manuscripts of the New Testament, playing a crucial role in the creation of modern critical editions such as the Nestle-Aland Novum Testamentum Graece. These codices provide a textual basis that is considered closer to the original New Testament writings than the later Byzantine text-type."
Encyclopedia of Textual Criticism:
"The importance of Codex Vaticanus and Codex Sinaiticus in New Testament textual criticism cannot be overstated. Both manuscripts are heavily relied upon in the Nestle-Aland 28th edition, which seeks to reconstruct the earliest attainable text of the New Testament."
Christianity Today:
"Modern critical editions of the Greek New Testament, like the Nestle-Aland 28, draw extensively from Codex Vaticanus and Codex Sinaiticus. These manuscripts, due to their early dates and high quality, are pivotal in establishing the Alexandrian text-type, which is often regarded as closest to the original New Testament writings."
Daniel B. Wallace:
Daniel B. Wallace highlights that the NA28, like its predecessors, is primarily an eclectic text, drawing heavily from Vaticanus and Sinaiticus. He notes that while the NA28 uses over 5,000 manuscripts, the readings from Vaticanus and Sinaiticus are often prioritized, with many other manuscript readings being disregarded when they conflict with these two.
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Daniel B. Wallace).
James Snapp, Jr.'s Blog:
NA most definitely is an eclectic text; it is eclectically drawn from the texts of B [Vaticanus] and ℵ [Sinaiticus] (A in Revelation), with occasional resort to D, L, and a minuscule or two where those three do not supply a reading. So yes, the 'eclectic' compilation, though its supporters boast is based on over five thousand Greek manuscripts, is actually based on about five manuscripts. Readings found in as many as 3000 other manuscripts are routinely ignored whenever they differ from the united testimony of B and ℵ."