The 9x63 predates both the Steigleder catalog and the .35 Whelen by some years, it is even older than the 63mm case length of the .30-06! The cartridge was also named the 9x63 Florstedt , a widely publicized cartridge before WWI. An original cartridge I have seen had a longer neck than the 9.3x62, about like the 35 Whelen. A few years ago at a shooting range I met a man who happily sighted in his inherited Miller & Greiss 9x63 98 Mauser sporter with Remington .35 Whelen factory loads, his cases did not look unusually distorted. The cartridge/load was named for Alexander Florstedt,see photo, an early-1900s gentleman hunter and scribe, who hunted the Carpathian and Alpine mountains as well as those of Asia. The Carpathes as well as large parts of Poland and Ukraine were then part of the Austro- Hungarian empire.
In his book "Jagen in den Hochgebirgen Asiens und Siebenbuergens" he writes: "The 9x63 was first special order loaded for me by RWS with 3.5g = 54grs of powder and a light 23mm long bullet several years before the war/WW1. It was the best high-mountain-game cartridge of those days." Internal evidence in his writings points to 1903, when he got his rifle from Miller&Greiss in Munich. He does not give bullet weight or ballistics, but an contemporary RWS bullet catalog gives weights around 200 grs for 23mm bullets, from 185 to 215, depending on shape. So the .35 Whelen existed many years before Colonel Whelen or Mr.Howe invented it.