So let me understand your position. Since the earliest codices that we have of the Septuagint with Deuterocanonical books date from the 4th/5th century, the Deuterocanonical books must have been added by the Christians. And this is backed up by the fact that Aquila’s Greek version, which was made in the 2nd century when the Jews had rejected the Septuagint because of its use by Christians, does not include them. Additional evidence is an 11th century manuscript of a list of the books of the Old Testament.
This is pure speculation or even wishful thinking. At the end of the day the earliest complete codices we have of the Septuagint contain the Deuterocanonical books, and there are no complete codices of that period the are missing them. The question also arises, if the Deuterocanonical books were only added by the Christians in the 4th century to an earlier received Old Testament without them, who added them and why does the manuscript evidence only show their inclusion?
The pure speculation or even wishful thinking is that the 1st. LXX contained them. Aquila is merely one aspect of the argument that the LXX of the 1st century, and related to more and more importantly, that the body of writings refereed to as "Scripture" by the Lord and NT church, did not include the Deuteros as Scripture In review
manuscripts of anything like the capacity of Codex Alexandrinus were not used in the first centuries of the Christian era
the order of the books in the great fourth and fifth-century Septuagint codices is Christian, not adhering to the three divisions of the Hebrew canon;
Moreover, all three codices [Vaticanus, Sinaiticus and Alexandrinus], according to Kenyon, were produced in Egypt, yet the contemporary Christian lists of the biblical books drawn up in Egypt by Athanasius and (very likely) pseudo-Athanasius are much more critical, excluding all apocryphal books from the canon, and putting them in a separate appendix.
Jewish historian Flavius Josephus appears to be the earliest extant witness to this view. Answering the charges of an anti- Semite Apion at the end of the first century of our era, he says: “
We do not possess myriads of inconsistent books, conflicting with each other. other. Our books, those which are justly accredited, are but two and twenty, and contain the record of all time....” — Josephus, Against Apion, 1,8 (38-41) On the basis of later Christian testimony, the twenty-two books mentioned here are usually thought to be the same as our thirty-nine,2 each double book (e.g., 1 and 2 Kings) being counted as one, the twelve Minor Prophets being considered a unit, and Judges-Ruth, Ezra-Nehemiah, and Jeremiah-Lamentations each being taken as one book. This agrees with the impression conveyed by the Gospel accounts, where Jesus, the Pharisees, and the Palestinian Jewish community in general seem to understand by the term "Scripture" some definite body of sacred writings."
"In all likelihood Josephus' twenty-two-book canon was the Pharisaic canon, but it is to be doubted that it was also the canon of all Jews in the way that he has intended."
By the first century, it is clear that the Pharisees held to the twenty-two or twenty-four book canon, and it was this canon that eventually became the canon of Rabbinic Judaism because the majority of those who founded the Jewish faith after the destruction of Jerusalem were Pharisees. The Jewish canon was not directed from above but developed from the "bottom-up." (Timothy H. Lim, University of Edinburgh)
"...the pseudepigraphical work 4 Ezra (probably written about A.D. 1208)...admits that only twenty-four Scriptures have circulated publicly since Ezra's time.
The Catholic Encyclopedia itself affirms the Palestinian canon as consisting of the same books. “the protocanonical books of the Old Testament correspond with those of the Bible of the Hebrews, and the Old Testament as received by Protestants.” “...the Hebrew Bible, which became the Old Testament of Protestantism.” (The Catholic Encyclopedia>Canon of the Old Testament; htttp://www.newadvent.org/cathen/03267a.htm) The Protestant canon of the Old Testament is the same as the Palestinian canon. (The Catholic Almanac, 1960, p. 217) (http://www.newadvent.org/cathen/03267a.htm) The available historical evidence indicates that in the Jewish mind a collection of books existed from at least 400 B.C. in three groups, two of them fluid, 22 (24 by another manner of counting) in number, which were considered by the Jews from among the many other existing books as the only ones for which they would die rather than add to or take away from them, books which they considered veritably from God...The Apocrypha are not included. (http://www.biblicalstudies.org.uk/pdf/rev-henry/11_apocrypha_young.pdf) For the Jews of Palestine the limits of the canon (the term is Christian, and was not used in Judaism) were rigidly fixed; they drew a sharp line of demarcation between the books which 'defiled the hands', i.e. were sacred, and other religiously edifying writings.- J. N. D. Kelly That there was an established authoritative body of writings of God by the time of Christ is manifest by the frequent quotes or references to them as authoratative by the Lord Jesus and the NT writers. Which was never manifest as being an issue with the Scribes and Pharisees whom the Lord affirmed sat in the magisterial seat of Moses, (Mt. 23:2) to whom conditional obedience was enjoined. There is also further testimony, but this should suffice as evidence that the established most authoritative body of writings of God by the time of Christ was not that of the expanded canon seen in late LXX MSS, and yet which do not agree with Rome's Sources.
At the end of the day historical testimony is toward the Deuteros not being part of after the 1st century LXX, nor part of the most authoritative canon, with the two being related, and with Christ reference to the tripartite canon in Lk. 24:44 (and as "all Scripture" in v. 27) being that one.
Thus the reason there are no complete codices that are missing the Deuteros is because the earliest complete codices are hundreds of years after 132 B.C. and the 1st century LXX, and some Christian are known to have messed with it. Yet even then the codices conflict with each other and with Trent on the issue of the contents.
Also, seeing as the last books of the Deuteros are thought to have been written some time around 100 BC (or later) while the translation of the Septuagint itself was completed by 132 BC then it leaves little time for the establishment of them as Scripture proper.
The question also arises, if the Deuterocanonical books were only added by the Christians in the 4th century to an earlier received Old Testament without them, who added them and why does the manuscript evidence only show their inclusion?
Look at your question. The answer to the last sentence is in the first one. "Christians" added them which is why the manuscript evidence from hundreds of years later show them, while the Palestinian Hebrew canon, which what Christ only quoted from, did not. To suppose otherwise is more wish than substance.