The first Christians weren't Bible Christians

[Aractus]

What you said about the Catholic Church not knowing what the correct canon was until the 16th Century is a cherished myth void of truth and can easily be proven so.

You haven't tried to trace the history of the LXX and Apocrypha. If you had this would be a very different discussion. The Latin Vulgate has its own Apocrypha section of three books rejected from the scriptures at the time, banished from the canon, and still rejected by Catholics, Protestants and Jews.

The Jewish canon can be traced all the way back to Christ very nicely. It is arranged into 3 sections - "Law", "Prophets" and "Writings"/"Psalms". There's overwhelming evidence for this, and this is the version of scriptures that Jesus is familiar with:

• Luke 24:44: Then (Jesus) said to them, “These are my words that I spoke to you while I was still with you, that everything written about me in the Law of Moses and the Prophets and the Psalms must be fulfilled.”

The structure of the LXX is different and is: Law, History Wisdom, Prophets. We can trace the Hebrew structure as it is in the MT back before Christ, we can trace the LXX structure to the 5th column of the Hexapla, that's where the order comes from, and in fact that's the first time we ever find the Apocrypha alongside the scriptures (as you mentioned, Tobit was found in the DSS alongside scriptures and plenty of non-scriptures). We never hear any mention of these 4 categories until the Hexapla.

There are six bodies of text that contemporary scholars consult for the Old Testament:

1. Masoretic Text (10th century)
   
2. Qumran Text (2nd cent BC-2nd cent AD)
   
3. Samaritan Pentateuch (composition c. 200-100 BC, earliest copy 11th century AD)
   
4. Septuagint (composition c. 1st cent BC-2nd cent AD - no complete ancient manuscripts of the LXX) Main Manuscripts: Codex Marchalianus (6th cent.), Codex Vaticanus (4th cent.), Codex Sinaiticus (4th cent.), Codex Alexandrinus (5th cent.), Codex Ephraemi Rescriptus (5th cent.) and, finally Codex Chisianus (9th cent. and the only manuscript to contain the LXX book of Daniel as it appeared in the Hexapla, besides the fragmentary P967).
   
5. The Peshitta (Syriac, Authors unknown, date unknown).
   
6. Vulgate (Latin, early 5th cent. the primary textual basis for the OT followed the LXX as it appeared in the Hexapla with the exception of Daniel which followed Theodotion's Daniel).

The other Greek translations - aside from some of Theodotion's - have been forever lost. While Theodotion translated the whole of the OT, it is known he did not include the apocrypha, aside from Baruch.

What you call the LXX has been shortened anyway, originally the LXX included the Prayer of Manasseh, 3 Esdras and 4 Esdras which ever since the Vulgate has forever been banished to non-canon status.

In any case the LXX traces back to the Hexapla, where it is beyond doubt that Origen substantially modified it as he went along (he even marked the areas that he changed). Jerome himself attests to this fact.