Bible (OT) Was Completely Lost
We can read in the verse below that after the House Of Israel came back to Jerusalem they found a book in the walls of the old temple and assumed that it was the “book of the laws” (Old Testament – five books of Moses).
2 Kings 22:8-16 - And Hilkiah the high priest said unto Shaphan the scribe, I have found the book of the law in the house of the LORD.
King then appoint some people to find out this book is really the book of the laws. So clearly it says they did not know if it was the OT. They did not have any other book of the laws to compare with and come to the conclusion that it was (or not!). So it is clear that they did not have any of the book of Moses anymore.
II Kink 22:13
13 Go ye, inquire of the LORD for me, and for the people, and for all Judah, concerning the words of this book that is found: for great is the wrath of the LORD that is kindled against us, because our fathers have not hearkened unto the words of this book, to do according unto all that which is written concerning us.
They go to the Huldah the prophetess (verse 15) and she tells them:
II King 22:16
16 Thus saith the LORD, Behold, I will bring evil upon this place, and upon the inhabitants thereof, even all the words of the book which the king of Judah hath read:
It is only because Huldah the prophetess conform that yes it is the book of the laws of Moses that they accept it as the OT that they no longer had any copy of.
You can find the same events explained above at:
2 Chronicles 34:14-24 - And when they brought out the money that was brought into the house of the LORD, Hilkiah the priest found a book of the law of the LORD given by Moses. And Hilkiah answered and said to Shaphan the scribe, I have found the book of the law in the house of the LORD. And Hilkiah delivered the book to Shaphan.