'the outer books') are religious texts written in large part by Jews, especially during the Second Temple period, not accepted as sacred manuscripts when the Hebrew Bible was canonized.
Based on unfulfilled prophecies, these books were not considered scripture, but rather part of a literary form that flourished from 200 BCE to 100 CE.
These works usually bore the names of ancient Hebrew worthies to establish their validity among the true writers' contemporaries.
2 Esdras reinforces this theory: when Ezra was inspired to dictate the sacred scriptures that were destroyed in the overthrow of Jerusalem, So during the forty days ninety-four books were written.
And when the forty days were ended, the Most High spoke to me, saying, "Make public the twenty-four books that you wrote first and let the worthy and the unworthy read them; but keep the seventy that were written last, in order to give them to the wise among your people.