As with all of Tolkien’s great tales of the First Age, the story of Beren and Lúthien transformed dramatically over sixty years from its first imagining and version in 1916 and 1917 to its relatively finalized version in 1977’s The Silmarillion. During those six decades, it appeared as a long tale of the Lost Tales, as a summary in the 1926 Sketch of the Mythology (written for Tolkien’s beloved professor from King Edward’s, R.W. Reynolds), as a radically ambitious poetic lay, The Lay of Leithian (1925-1931), and as an essential story within the various versions, including the final version, of The Silmarillion.

Yet, the essence of the story has remained the same in all of its many versions. Or, as Christopher so wisely put it, “The fluidity should not be exaggerated: there were nonetheless great, essential, permanences.”
— Read on theimaginativeconservative.org/2019/08/jrr-tolkien-beren-and-luthien-bradley-birzer.html