Tolkien's Oriental Sources? Renunciation of Immortality and Fairy Nature

Thompson motif F302.6.2.2. Fairy gives up her fairy nature and becomes mortal to be able to return to her mortal husband and its combination with H310. Suitor tests and H1010. Impossible tasks are Oriental motifs, to be found only in the Tibetan tale of The Boy with the Deformed Head in O'Connor's 1907 collection and in the 9th century CE Japanese Taketori Monogatari. In this light, it appears necessary, assuming that Tolkien had a source for his idea of Lúthien sacrificing her Elven immortality and Elven fate, that his source must be found in the aforesaid narratives, both available in English before he started writing "The Tale of Tinúviel," the earliest form of his legend of the Elf-maiden and her human lover.