Here is the detailed text from Houghton-Mifflin.

…The forthcoming paperback set of the History of the Lord of the Rings, which ships August 3rd, is technically a subset of the History of Middle-earth and is available in the U.S. in paperback for the first time.

Those familiar with the 9th volume of the Middle-earth series in hardcover (Sauron Defeated) will know that it contains The Notion Club Papers and other material that does not pertain specificly to LotR. For this new paperback boxed set, called the Hist of LotR, the non-LotR material has been cut out of volume 9 to create a “new” book called The End of the Third Age, which has been re-indexed. THAT book, EofTA, will only be $12, not $50 as reported.

The full set of the paperback editions, Return of the Shadow ($14), Treason of Isengard ($14), War of the Ring ($14), and End of the Third Age ($12) will be offered in as a box set for $50, and is designed to match Houghton Mifflin’s current four-volume boxed set of LotR and The Hobbit…

Happy reading! It’s always a pleasure to find ‘new’ Tolkien material coming into circulation.