Tolkien first wrote down the Tale of Tinuviel in 1917 -- see Beren IV's
discussion, possibly, in the next few days, more details may emerge.
In the mid to late 1920s, Tolkien wrote the Lay of Leithian in verse form,
making major changes to the Tale; primarily, Beren was reconceived as a Man,
earlier he had been a more primitive or rustice elf. Also, the Sauron character
becomes a great Necromancer instead of an evil Cat.
In hopes of having 20 years' work published after the success of The Hobbit,
Tolkien made a major effort to transform his Silmarillion myth-cycle into a
coherent prose narrative in 1937. Although he had made a quick precis in 1930
(called the Quenta in Vol IV of HoME, The Shaping of Middle-earth), this
was far more completely written out, and is referred to as the Quenta
Silmarillion in Vol V of HoMe, The Lost Road and Other Writings. What
Christopher Tolkien notes in his editing of the Quenta Silmarillion, is that
the Tale of Luthien seems to get out of hand. It threatens, in its length and
complexity, to overwhelm the complete Silmarillion. Tolkien sputters and
restarts several times in his prose rendering of the Tale - what had been a
very clean manuscript up until Luthien becomes a series of rough drafts as
Tolkien struggles to compress Luthien and Beren into the Silmarillion at an
acceptable length. Nevertheless the vast majority of the Tale of Luthien and
Beren as seen in the published Silmarillion (1977) stems from the 1937 effort
by Tolien -- which is totallly based on the Lay of 1926-30, and of which many
ideas, never afterward explicitly changed, come directly from the first, far
more Fairy-taleish, Tale of Luthien,
1917.
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