Oy, where should I start? Erasmus used several Greeks sources, but none was a complete New Testament. He relied heavily on the Vulgate as well as his own Latin translation. His first edition, finished in one yer [!], was a complete failure, I hope we can agree on that (including the title Instrumentum instead of Testamentum). His second edition was apatch-up job.
His third edition contained even Comma Johanneum (whose originals can be traced to Latin Fathers, retro-translated into Greek). This third copy was used by Tyndale to translate into English.
His fourth and fifth editions were based on the Polyglot Bible, at which time he dropped the Vulgate. The Greek sources he used originally are who knows from where. The Greeks sources don't always agree either, depending whether they are the Byzantine or Alexandrian type.
The Codex Vaticanus and Sinatius are in agreement, but the Codex Alexandrinus (the one used by the Orthodox Church) is somehow more "Christianized."
Then there is the "Jewish Bible" in addition to our various version of the NT. The only thing they all have in common are names of the Books.
Let me illustrate:
Isaiah 9:6
For a Child is born to us, and a Son is given to us, whose government is upon His shoulder; and His name is called The Messenger of Great Counsel; for I will bring peace upon the princes, and health to Him. [The Septuagint, Brenton]
For unto us a child is born, unto us a son is given: and the government shall be upon his shoulder: and his name shall be called Wonderful, Counsellor, The mighty God, The everlasting Father, The Prince of Peace. [KJV, NA27]
Sinatius=Sinaiticus
That might explain why Erasmus, Stephanus, and Beza used some of the old Latin texts for some of the readings of the Epistles because the old Latin had been translated from the original Byzantine Text and they needed it to get those original Byzantine text readings in the Epistles.
BTW Erasmus had atleast five Greek manuscripts dating from the 11th to the 15th century. He used these to make his own Latin version in 1505, and for his later Greek texts. His Greek text came from Greek manuscripts not the Vulgate --- except for the Johannine Comma and perhaps a few others.