The only thing I know about it is that it took place in 1929 and the only name in the trio of first ascenders that rings a bell is Willi Merkl. He was one of Europe's best mountaineers of the time. Unfortunately Merkl died on an ill fated expedition to Nanga Parbat in 1934. Koshtan was the last of the Caucasian peaks over 5000m to be climbed, if I remember right. Merkl was the step- or half brother (don't remember which) of Karl Herrligkoffer.
Many of the Caucasian peaks were climbed by central Europe's top mountaineers. For ex. Kokkin was there already in the 1880's climbing a lot of important peaks.