8 And Hilkiah the high priest said to Shaphan the secretary, “I have found the Book of the Law in the house of the Lord.” And Hilkiah gave the book to Shaphan, and he read it. 9 And Shaphan the secretary came to the king, and reported to the king, “Your servants have emptied out the money that was found in the house and have delivered it into the hand of the workmen who have the oversight of the house of the Lord.” 10 Then Shaphan the secretary told the king, “Hilkiah the priest has given me a book.” And Shaphan read it before the king. 11 When the king heard the words of the Book of the Law, he tore his clothes. 12 And the king commanded Hilkiah the priest, and Ahikam the son of Shaphan, and Achbor the son of Micaiah, and Shaphan the secretary, and Asaiah the king's servant, saying, 13 “Go, inquire of the Lord for me, and for the people, and for all Judah, concerning the words of this book that has been found. For great is the wrath of the Lord that is kindled against us, because our fathers have not obeyed the words of this book, to do according to all that is written concerning us.” 2 Kings 22:8-13
Israel forgot about the contents of the written Torah. It was discovered in the Temple and the message caused a reaction in the king.
What does this text show us? If they forgot about what was in the written Torah, I'm going to assume they forgot the Oral Torah. And you don't have a written text with the Oral Torah to recover that knowledge.