I assume you are questioning why the Hebrew and Targum texts are not used over the Septuigent. The thing is that Christ and the Apostles used and referred to the Septuigent. In 300 CE the Sadducees redacted the scriptures using dubious criteria which had nothing to do with inspiration, but the council of Hippo maintained the Septuigent as the complete Old Testament Canon.
One of the questioned books is Tobit. It was rejected by the Sadducees for not being written in Hebrew. 1900 years later, a 2400 year old copy in flawless Hebrew was found. If the Sadducees had gotten their hands on it in 300 Tobit might have made it into the Hebrew canon.
In Qumran the scrolls were housed with other literature, not found in the canon. On my bookshelf, you will find my NAB Bible, annotated concordance, a bible study text, quotes from Mother Teresa, and the book of Mormon. Only the Bible is inspired. The rest is good pious reading except for the book of Mormon which is not. Same thing with the scrolls of the Essenes, the Biblical books are inspired, the other books like the Assumption of Moses are heartening, pious literature but do not rise to the level of ‘‘Inspired’’ and of course the heretical gnostic teachings which was not a Christian heresy but an errant philosophy that contaminated Semitic and Christian faiths.
But that’s all ancient history…