My particular version, which I bought around 30+ years ago, is a "Philharmonia" study score. According to the inside title page, the Philharmonia series was apparently a subsidiary of Universal Edition, though at the time I bought it, I don't know if there was a full-price Universal Edition score available, nor can I tell you if the Philharmonia version was a less-expensive version of the Universal Edition. The English translation of the German introduction states that "this pocket score is a photo-mechanical reproduction of the whole text of the symphony from the complete works of Gustav Mahler, edited by Erwin Ratz (Kritische Gesamtausgabe, vol. X). In this text the original - more or less corrupted in earlier editions - has been resored on the basis of authentic source material and scrupulous editing procedures to conform to Mahler's intentions".
If you intend to look for this Philharmonia edition, I can't tell you if it is still available, or if the full-price Universal Edition has superseded it. By way of caution, the less-expensive Dover full-size score might not have any updates that the Universal Edition might have. Barry might have something to say about this, if he has a study score of the 9th.
Wade