Did the pre-Christian Greek Bible contain only the five books of Moses? The New Testament quotes portions of the Greek Old Testament (known as the Septuagint, or LXX for short), including portions of books beyond the Pentateuch (or five books of Moses), some of which are of a distinct tradition than that of the Hebrew (or what is loosely called the Masoretic tradition).1

Yet it is claimed by Jews,2 as well as others, that the Septuagint was originally only a translation of the five books of Moses, not the entire Bible.

Question: If this is so, what exactly were the New Testament authors quoting?

Thanks in advance.



Footnotes

1 e.g. Mt 9:13 "mercy" (LXX) / cf. Hos 9:6 "goodness" (Masor); Mt 9:13 "perfected praise" (LXX) / cf. Ps 8:2 "ordained strength" (Masor). See also Mk 7:6-8/Isa 29:13; Lk 3:5-6/Isa 40:4-5; Rom 2:24/Isa 52:5 | It's been estimated that out of all the quotations of the Old Testament in the New, 340 are from the LXX, and 33 from the Masoretic (see G. Archer and G. C. Chirichigno, Old Testament Quotations in the New Testament: A Complete Survey, p. 25-32).

2 The 1906 Jewish Encyclopedia (Bible Translations, under 'Septuagint') states, "According to Aristeas, the Pentateuch was translated at the time of Philadelphus, the second Ptolemy (285-247 B.C.), which translation was encouraged by the king and welcomed by the Jews of Alexandria. Grätz ("Gesch. der Juden," 3d ed., iii. 615) stands alone in assigning it to the reign of Philometor (181-146 B.C.). Whatever share the king may have had in the work, it evidently satisfied a pressing need felt by the Jewish community, among whom a knowledge of Hebrew was rapidly waning before the demands of every-day life. ¶ It is not known when the other books of the Bible were rendered into Greek. The grandson of Ben Sira (132 B.C.), in the prologue to his translation of his grandfather's work, speaks of the "Law, Prophets, and the rest of the books" as being already current in his day. A Greek Chronicles is mentioned by Eupolemus (middle of second century B.C.); Aristeas, the historian, quotes Job; a foot-note to the Greek Esther seems to show that that book was in circulation before the end of the second century B.C.; and the Septuagint Psalter is quoted in I Macc. vii. 17. It is therefore more than probable that the whole of the Bible was translated into Greek before the beginning of the Christian era (Swete, "An Introduction to the O. T. in Greek," ch. i.). The large number of Greek-speaking Jewish communities in Palestine, Syria, Mesopotamia, Asia Minor, and northern Africa must have facilitated its spread in all these regions. The quotations from the Old Testament found in the New are in the main taken from the Septuagint; and even where the citation is indirect the influence of this version is clearly seen. This will also explain in a measure the undoubted influence of the Septuagint upon the Syriac translation called the "Peshiṭta.""
No, the entirety, more or less,1 of the Old Testament seems to have had a Greek version or translation since the second century at least, based on the translator's Prologue to the Greek version of Ben Sira (a.k.a Wisdom of Sirach and Ecclesiasticus).
In a collection of papers on the Book (from 2006),2 it is taken for granted that the rest of the Books of the Old Testament already existed by the second century B.C., in what we would (loosely) call a Septuagint version, that is, the Greek Old Testament.
Discussing the translator's own feeling that the Greek into which he was translating the original Hebrew did not have &quot;the same force&quot; (ισοδψναμει) (Prologue) as the original language itself (the Hebrew), the author of one paper3 writes:

In [his prologue] the grandson of Ben Sira brings the Biblical books as an example for the difference between original and translation:

ου μονον δε  ταυτα αλλα και αυτος ο μονος και αι προφητειαι και τα λοιπα των βιβλιων ου μικραν εχει την διαφοραν τον εαυτοις λεγομενα (&quot;That is true not only for this book but also the Law itself, the Prophets, and the rest of the books differ no little in the original.&quot;)

The way the Hebrew original is introduced at the end of the argument shows that the comparison proceeds from the Greek and not from the Hebrew version of the Law, the Prophecies, and the remaining books. This proves, that the grandson of Ben Sira believed his Greek readers to be familiar with the Greek version of these books, but ignorant of the Hebrew text.

(emphasis mine)
I think from this we have a strong case for the existence of an entire Greek Old Testament, not just the Law or Torah; as well as a readership aquainted with it, and even ignorant of the orginal Hebrew (if not Hebrew itself, then at least the original Hebrew versions themselves). We are left to opine as to who this readership is, although Alexandrian or Diaspora Jews (cf. Jn 7:35; Jas 1:1; 1 Pet 1:1) fit the bill quite well.4

1 Unfortunately, based on the following alone as the evidence, we cannot be more specific. In the least, every section of the Old Testament was completed.
2 Studies in the Book of Ben Sira (Géza G. Xeravits, Jószef Zsengellér), 2006.
3 ibid. p. 51. &quot;The Pre-eminence of the Hebrew Language and the Emerging Concept of the 'Ideal Text' in Late Second Temple Jerusalem&quot; (a paper by Stefan Schorch)—I had to transcribe the quote myself, so I couldn't include breathing marks and so forth, whereas the original has such. The author seems to have made a typographical error, having &quot;Prophecies&quot; were it should say &quot;Prophets&quot;(especially in concordance with what precedes it, and the fact that the first letter is upper-case. He also omits a what would be a heplful ellipsis after the Greek; the rest of the sentence continues: &quot;[have no small difference,] when they are spoken in their own language.&quot;
4 &quot;[I]...using great watchfulness and skill in that space to bring the book to an end, and set it forth for them also, which in a strange country are willing to learn, being prepared before in manners to live after the law&quot; would seem to imply a Jewish readership.