If they did use it they would not have used it in Israel where the Jews spoke Hebrew and the Hebrew Text was authoritative. And the Jews that wanted to make sure that the Apostles were telling the truth about the prophecies of the Messiah would have checked with their most authoritative copy --- the Hebrew Text, not a translation, Greek or otherwise. The Hebrew Text was the official text.
All we know for sure, from those like Josephus and Philo, is that the Septuagint, which was primarily only the five books of the Law, was used by the Hellenistic Jews of Alexandria.
Obviously, in only six instances did they prefer clearly the Hebrew (Pharisaical) version of the OT as opposed to that of the LXX.
But you and every other Septuagintist knows very well that there is no proof that the Septuagint that you have in your hands today to make these claims is the same Septuagint that was in the hands of the Hellenistic Jews of Alexandria at the time of the Apostles, or even in the hands of the Christian Church before the time of Origen. You have no pedigree and the facts of history are against you. Otherwise why would Christians be using Aquila's, or Symmachus', or Theodotian's Greek OTs if there had been a sacred Septuagint text available. And why would Origen need these translations for his fifth column or even a fifth column LXX at all if a Septuagint existed in any viable form???And why spend years and money and 5000 pages of valuable papyrus to create something that already existed???
According to Paul Kahle, the famous OT scholar, who did extensive work on the Septuagint, there was no single Greek version or archetype, just a variety of Greek translations. Only later was an official standardized version of the Law made, but for the rest of the books, there were a variety of translations. As he said, the later formulators of the Greek OT made it conform with the New Testament Text, and thus the Septuagint that you have in your hand quotes from the New Testament, not vice versa.
Actually, the use of the Septuagint was quite common even in Palestine in the first century AD. However, the Epistles were written for the Gentiles and hellenized Jews of Asia Minor, and the Gospels followed when the Church was already in exile, and were intended for the Gentile converts, so using a Hebrew source was pointless.
the later formulators of the Greek OT made it conform with the New Testament Text, and thus the Septuagint that you have in your hand quotes from the New Testament, not vice versa
If that is so indeed, then a vast number of references made by the Apostles to the OT become meaningless, since they differ in meaning and content from those in the Hebrew Bible.
The same would hold true of Matt 1:23, where Christian Bibles specifically use the word "virgin" and not "a young woman."1
Is that not an example where all Christians "adjust" the New Testament to fit the Old?
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1The Hebrew word for young woman Isaiah used is 'almah, and the Greek word is korasion. The Hebrew word for virgin is bethuwlah, and the Greek word parthenos. The Septuagint uses parthenos in place of 'almah.
The same is true of many other words we use, starting with the word Messiah. The meaning of the Hebrew word meshiyah is unlike anything we assign to it. Other phrases commonly encountered such as the "world to come" have been "retro-engineered" by Christian founders to mean something they never meant in Judaism.
Frankly, accusing the Orthodox of retro-fitting the OT to agree with the NT is like the pot calling the kettle black, since all of Christianity is based on finding the "foreshadowing" of Christ in the OT which the Jews deny as much as Christians deny LDS to be a 'fuller' revelation of Christ.
All of Christianity is 'retro-fitting' Judaism to fit the NT, imo, beginning with abandoning such practices as circumcision and dietary laws for the Gentiles. Christ never taught or even hinted at that. All that was later added ex post facto in Acts.
As for various versions of the Septuagint floating around, they were not Septuagint but Greek translations of the OT written by a convert to Judaism and an Ebonite apostate, masquerading as 'Septuagint.' The only one that was written by a Christian was a 3rd century translation from Ephesus. The Christians there did not ask for the Library of Congress verification of various books. People read what was available. If it was in Greek and it looked like the OT they assumed it was the Septuagint.
There were no copy-right laws. Among Christians, the people copied whatever they felt like copying and in any way they wanted. If the scribe felt the copy he was copying was flawed, he would insert a 'correction' of his own. We are not even sure of the authorship of some of the NT books, let alone of the veracity of the flood of stuff that came along centuries after.
Eventually, Christian texts were made more flawless and more seamlessly connected. The Codex Alexandrinus is a perfect example of such efforts, which coincided with the more elaborate theological definitions and practices of the Church. The resultant Christian canon by the end of the 4th century AD was a carefully screened and redacted set of books, with all the originals "conveniently" lost.