if the Septuagint for the entire OT existed and was considered accurate by the apostles, then why don't all the NT quotes of the OT follow the Septuagint???
You see, theologians will quote from Scripture which they find suits their purpose. In some cases, the Hebrew version was more suited for their purpose that they were writing about. In most cases, however, the Greek OT was quoted from, such as Is. 7:14.
Biblical scholars indicate that only the five books of Moses composed the Septuagint and the rest of it was translated during the Christian era. And the DSS nor anyone else can provide any evidence of a pre-Christian Septuagint.
Hardly true. There are well over one hundred allusions in the NT of the OT Deutercanonicals - no doubt taken from Greek writings of these books. Thus, the Septuagint preceded the NT.
Regards
According to Josephus and others the Septuagint in his day composed only the five books of THE LAW of MOSES.