Books

Edit Appears to be a 5th and final set, outside "The History of Middle Earth":

The Children of Húrin
Beren and Lúthien
The Fall of Gondolin
https://www.amazon.com/dp/0358003911

Significantly less expensive than the others. Those also appear to be the final three books edited by Christopher Tolkien.

Three more books follow:

The Nature of Middle-earth, edited by Carl F. Hostetter.

https://tolkiengateway.net/wiki/The_Nature_of_Middle-earth

"Its many texts discuss a variety of topics related to Middle-earth, such as its "nature" and landscapes, the characteristics of different races, theology, and many other miscellaneous matters in Tolkien's legendarium. Most of them were previously unpublished material, but some had been already published in the linguistic journals Parma Eldalamberon and Vinyar Tengwar."

The Fall of Númenor, edited by Brian Sibley.

https://tolkiengateway.net/wiki/The_Fall_of_N%C3%BAmenor

"The texts were previously published in The Silmarillion, Unfinished Tales, The History of Middle-earth, and The Nature of Middle-earth, edited by Christopher Tolkien and Carl F. Hostetter. No new material by Tolkien is presented in this book."

The Battle of Maldon: together with The Homecoming of Beorhtnoth, edited by Peter Grybauskas.

"The book presents for the first time Tolkien's own prose translation of "The Battle of Maldon", a 10-century Old English poem about a real world battle, together with the poem The Homecoming of Beorhtnoth, an imaginary sequel to the Battle. Also included is a previously unpublished lecture "The Tradition of Versification in Old English", which deals with the nature of poetic tradition."

Looks like parts of it are in this set, but this book is it's own thing.

https://tolkiengateway.net/wiki/The_Children_of_H%C3%BArin

"A brief version of the story formed the base of Chapter 21 of The Silmarillion, setting the tale in the context of the wars of Beleriand. Although based on the same texts used to complete the new book, Christopher Tolkien abridged the tale to avoid overcharging his edition.

Other incomplete versions have been published in previous publications:

The "Narn i Hîn Húrin" in Unfinished Tales.

Items in The History of Middle-earth series, including:

"Turambar and the Foalókë", from The Book of Lost Tales: Part Two

"The Lay of the Children of Húrin" (a narrative poem), from The Lays of Beleriand

None of these writings forms a complete and mature narrative. The published Children of Húrin is essentially a synthesis of the Narn and of the account found in The Silmarillion."