Deets (Edited November 2023)
The timeline of Tagore's life and work published at the Rabindrasarani website has an entry under November 1892 that states:
The short story Jay Parajay
Few pieces by Rabindranath are published in the Sadhana – Kartik issue, including the short story Jay Parajay.
Presumably a few rather than few is meant. Sādhanā was a Bengali literary magazine published by the Tagore family beginning November 1891. Rabindranath's essays, poems, and stories comprised most of the material therein.
Jadunath Sarkar's translation of this story, which appeared in The Modern Review vol. 10 no. 6, December 1911 under the title "Victorious in Defeat", is available on Wikisource. A note preceding the translation says:
Original story (জয়পরাজয়) first published in Sadhana, Kartik 1299 B.E. (October-November, 1892).
Subsequently, Tagore's own translation of the story, entitled "The Victory", appeared in a 1916 collection, The Hungry Stones and Other Stories. The preface states that "The Victory" was translated by Tagore himself. Further bibliographical information is not provided. There is no discussion of Sarkar's translation, so it is not clear why Tagore chose to retranslate the story himself. Nor is there any indication whether Tagore's translation had been previously published elsewhere. However, Pulinbihari Sen and Subhendusekhar Mukhopadhyay's far from definitive bibliography of English translations of Tagore's works, which appeared in a 1960/1961 volume of Indian Literature, does list this as the first appearance of Tagore's translation of the story.
The Bengali original of "The Victory", জয় পরাজয় (Jay Parājay, "Victory and Defeat") reappeared as part of the first volume of a multi-volume collection called গল্পগূচ্ছ (Galpaguccha, "A Bouquet of Stories"), published in 1926. A Bengali calendar month and year are given at the end of the story: কার্তিক ১২৯৯ (Kārtik 1299). That date, corresponding to late October or early November 1892, confirms both the Rabindrasarani timeline entry and the headnote to Sarkar's translation.
Presumably this is the date of composition rather than of first publication.
Unfortunately, Galpaguccha v.1 provides no bibliographic information about the original publication of Jay Parājay or any of the other stories therein. It is unlikely that Jay Parājay remained unpublished for 34 years. For one thing, as mentioned in the question, Jadunath Sarkar's translation of the story had appeared in 1911 with the title "Victorious in Defeat". Sarkar must have come across the Bengali original somewhere. Of course it's possible, albeit improbable, that Sarkar was working off Tagore's unpublished manuscript.
- The magazine Sādhanā is not the same as Tagore's 1921 collection of essays, Sādhanā: The Realization of Life. As has been stated elsewhere, Tagore really needed to be more creative with his titles.
- Romanization of the Bengali script in the answer text follows IAST conventions. Ad hoc transliterations in quotations from websites are retained as is.