Several newly-discovered manuscripts of unpublished works by Ernő Dohnányi (1877–1960) and other documents in the University Library of Bratislava and the Slovak National Museum — Music Museum Bratislava refute the misconception that this city, the composer’s birthplace, is lacking in sources about him. These manuscripts from the estates of two dedicatees, the Archduchess Isabella and Mártha Rigele, offer fresh insights into Dohnányi’s compositional process, and particularly into the multiple revisions of his String Sextet, originally composed in 1893. Versions 1 and 2 of this Sextet, with geographically divergent manuscript locations in the British Library and at Florida State University, are compared here inasmuch as Dohnányi’s development into a mature composer is clearly demonstrable. The two manuscripts from the estate of the Archduchess Isabella, a set of parts reflecting all known revisions and an autograph transcription provide evidence to support this writer’s hypothesis that the score with title page dated 1896 is probably the final version. The Sonata stands as confirmation that by 1899 the composition had reached its final form in the mind of the composer. Excerpts from Dohnányi’s family letters cited here offer further insights into this period.