It would be a mistake to attribute all-encompassing inspiration to the LXX. For example, one wouldn’t jump to conclude that the LXX’s Genesis was directly inspired. Genesis was originally written in Hebrew, and THAT’s the inspired version of Genesis. The LXX is by and large a translation. However, it was trusted as ACCURATE, not necessarily INSPIRED.
The Church by virtue of her apostolic authority basically says which books in the LXX belonged to the body of inspired writings. She says that III and IV Maccabees, 1 & 2 Esdras and the Prayer of Manasseh are NOT inspired, but that the rest are.
But the Church says little or nothing about the word-for-word content, just the list of books. In other words, just because a book was in the LXX, doesn’t mean it was inspired.
Jesus most likely never quoted from the LXX. Jesus was a Palestinian, not Hellenistic Jew. He most likely quoted from the Hebrew scriptures. Those who wrote in Greek are the ones who quoted from the LXX. This does not point to the LXX’s inspiration, but only to its accuracy and reliability.
To bring it to modern times, the Church quotes the RSV, but she never says the RSV is inspired, merely accurate.
