IMHO we do not have any copy of the LXX, aside from fragments. What we have are rather late Greek versions of OT books. Our copies are long after the end of the NT. So I don't know how to know in many cases that what we are reading is not a reading adopted from the NT, rather from the ancient LXX made by Jewish persons long before the NT. So far as I know, all copies of the LXX made before the NT have perished. So what would a Christian do who lived in the 4th century AD for his OT in Greek? If the Lord Jesus or an apostle is represented as having referred to the OT with certain strings of Greek words, would not that Christian prefer that reading to the actual LXX, then incorporate it into his Greek OT? I think we must always consider that any reading in the ancient Greek OT could have come from a NT text, if the NT cites it. IMHO, we actually should not be calling our so-called LXX, the LXX at all. For that reason, I think that the attempt to determine if a NT author quoted the LXX or the Hebrew MT, is a vain endeavor. Technically speaking, no string of Greek words is a quotation of a Hebrew document; for a quotation must be exact or it is not a quotation. But if you bring Hebrew into Greek, it will be translated, not quoted. So we have no quotations of the OT in the NT at all (aside possibly from rare transliterations); the citations are Greek representations of the OT. -- Forgive me for digressing from the main thrust of the query above.