I don't think your citations are proof that the English name of Großglockner is Grossglockner. It looks to me like they had technical difficulty printing the ß, and printed the closest "feasible" thing, being "ss". Is there a ß in the books you cited, for instance in names? Vienna, Milan, Venice and Cologne are English names, and they're clearly different from the originals. Grossglockner isn't, in my opinion.