Yes..
If you have read the Silmarillion, then you have read within it the story of the Lord of the Rings, the great battle, and the destruction of the One Ring..
Much less detail, but the entire story and the aftermath is all there..
Likewise, there is a brief, general description of the tale of Hurin and his family also contained within the Silmarillion..
This tale, and the one from "Unfinished Tales", and other notes and writings by Tolkien, were combined, edited, etc., to create the new, "complete" book..