Dr. F. F. Bruce correctly points out that, strictly speaking, the LXX deals only with the Law and not the whole Old Testament. Bruce writes, “ The Jews might have gone on at a later time to authorize a standard text of the rest of the Septuagint, but . . . lost interest in the Septuagint altogether. With but few exceptions, every manuscript of the Septuagint which has come down to our day was copied and preserved in Christian, not Jewish, circles.” (The Books and the Parchments, p.150). This is important to note because the manuscripts which consist of our LXX today date to the third century AD. Although there are fragments which pre-date Christianity and some of the Hebrew DSS agree with the LXX, the majority of manuscripts we have of the LXX date well into the Christian era. And, not all of these agree.
http://www.purewords.org/kjb1611/html/lesson08.htm
The oldest complete bibles (with some books later discarded, i.e. Epistle of Barnabas, etc.) date to the 4th century. The oldest fragments (more like "shreds" containing a dozen verses) of various Gospels are copies of copies, the oldest one being John 1 dated c. 125 AD.
According to this logic (I agree with Bruce) copies of ciopies, removed hundreds ofyears from originals (if there were complete originals) is not enough to retro-engineer any piece of OT/NT without having the original.
Doing so, necessarily makes the Bible a human product. Also, the fact that some of the Hebrew language DSS agree with pre-Christian fragments of LXX shows that there was no single Jewish canon.
But we have already discussed this ad nauseum.