Correct. First Christians have no clue what 1st century Judaims was or what modern Judiams is. Second, Jewish scripture has been "canonized" from the very start because the only sacred books in the whole so-called "Old Testament" (Tanakh) are the five books of Moses, believed to be the Torah (or teaching) that was 'written' by God himself before the world existed. It is eternal and it cannot be fulfilled. It is the only part of the Jewish Bible that, when read, everyone stands. The rest of the Jewish Bible is secondary and only repeats what the Torah has already said. So, there was no need or urgency or desire to close the "canon," because THE canon is closed eternally. There is but one canon in Judaism and that is the Torah. Everything esle is only a repetition.