Aside from “because the Orthodox church says so” how do we know how many books were in the original LXX. Various mansucripts have different listing of books.
c.f.
geocities.com/Heartland/Pines/7224/Rick/Septuagint/sp_books.html
No one has the complete original orignal. Some have suggested that texts were later added to the LXX.
The scriptures were orignally scrolls and not a chunky book like to today. There were various OT and NT scriptures such as the book of Enoch (quoted in the NT), Obadiah (Not quoted in the NT), the Gospel of Thomas etc.
The Catholic canon for the OT (and NT) was decreed by the Pope at the council or Rome in 382 AD and was reaffirmed at countless other councils such as Hippo (393), Carthage (397 and 419), Nicaea II (787), Florence (1441), Trent (1545-1563), Vatican I (1869-1870), Vatican II (1962-1965) for example.
The Catholic Church’s canon does not rest on the LXX and She has never infallibly decreed how many books are in the LXX and thus has neither added nor deleted any book(s) from the LXX.
In what year did the Orthodox Church officially decree that the number of books for the OT? Do all Orthodox Christians agree?
The vulgate translated the Hebrew, Aramaic and Greek mansuscripts.
Lastly, someone mentioned something about book names…
Biblia Sacra (vulgate) aka in modern english translations
1 and 2 Kings aka 1 and 2 Samuel
2 and 3 Kings aka 1 and 2 Kings
Paralipomenon aka Chronicles
1 Esdras aka Ezra (2 Esdras Ch 1-10 LXX)
2 Esdras aka Nehemiah (2 Esdras Ch 11-23 LXX)
Ecclesiasticus aka Sirach