I do not understand you. Do you know what "codex" is?
Its a complete bible, i.e. Old testament and New testament in one "thing" => codex.
In the OT, there is Septuagint. Therefore, the codex vaticanus and sinaiticus are oldest complete copies of Septuagint.
What do you mean 'in the Old Testament, there is Septuagint'? The Old Testament was written originally in Hebrew and Aramaic. Not Greek. Any Old Testament written in Greek is a translation of the Hebrew. How good that translation is depends on the translator or translators.
'Codex' is just the putting of written pages in a book form in contrast to the older method of scrolls. Just because you have something labled as a codex in no way indicates it is a complete Bible. And neither Vaticanus or Sinaiticus are complete. Usually there is a third mentioned with these two called Alexandrinus. None are complete in themselves, though closer than any others.
That these are written in Greek, yes. Concerning the Old Testament, that makes them a translation of the Hebrew into Greek. Here, however, you assume they are a copy of a so called Septuagint. You assume this because you assume that there is a Septuagint. As I said earlier, the only proof of any existence of a Septuagint is the 'Letter to Aristas' which has been proved a fraud.
In reality, the story of the Septuagint was created to give some credibility to the Alexandrian Text, of which these two codex's you present, are part of. There were no 70 translators who miraculously translated the Old Testament into Greek in perfect agreement with each other. Vaticanus, Sinaiticus, and Alexandrinus, are what is known as the 'minority texts', also called the 'Alexandrian Text'. This is due to their place of origin, which was Alexandria.
Recognize these for what they are, which are Greek translations of the Old Testament and copies of the Greek in the New. For the New Testament was written in Greek. One is at the mercy of whoever wrote these as to their accuracy. Did he or they copy the New Testament correctly? Or did they add their own interpretation? This is why there is always comparison's made with other manuscripts.
The problem is that our modern day Bibles are based upon this Alexandrian Text, or the Minority Text. The King James Version was based on the Majority Text. In other words, our modern Bibles are based upon fewer manuscripts and these come from Alexandria. This itself is another problem.
But for now, it is important to know that there is no such thing as a Septuagint. It was a story created to give credibility to the Alexandrian text.
Quantrill