We figure that the JEWS ought to know their own scriptures a wee bit better than the claim that Rome does.
Which sect of Jews? The Jews who became Christian were largely the Greek-Hellenistic Jews, first and foremost was Saint Paul himself. Those who had access to the Greek-LXX version of the OT were the Jews more likely to believe in Christ and enter the Church. The Jews in Palestine, the ones holding to the Hebrew only tradition that the Rabbinical tradition grew out of in the late 1st and 2nd century were the Jewish groups who were more opposed to Christianity.
The Jews compiled the Septaguint a long time before the Masoretic compilation, BC, in fact whereas the Masoretic was a couple of centuries AD and avoided old accepted books that they thought might justify some Christian ideas. Mainline Protestants do seem to be taken with what is newer and more fashionable.
Second, you logically have find an authenticating authority on the texts (since the texts are not self- authenticating.) On the one hand, you have a group of Jews from a 7-10 century continuous tradition of rejecting Jesus as the Messiah, which I (as a Christian) would say is a 7 - 10 century tradition of misunderstanding their own Scriptures. (Sorry, That's how I see it.) They didn't just reject the 7 books of the Deutercanonicals. They rejected the whole 27 books of the New Testament.
On the other hand, you have a group of Christians with a 7-10 century continuous tradition of accepting Jesus as the Messiah. And you reject the Scripture specialists who say "Christ, Yes" and go with the ones who say "Christ, NO"?
????
Oy gevalt!