Dear Sir,
I'm pleased to know that at least on one point I'm holier than the Pope.
The gentlemen in question are very well known figures, one of them being Field-marshal and the other - general of cavalry. Men of such a posture deserved personal biografies written. So we know abou them much more than about a mere divisional commander. And in this question even the Wikipedia is correct.
Unfortunately the problem is well spread, when people are writing about the army without knowing the language. I heard of numerous such mistakes regarding Prussian or Austrian generals in 7 years war. But never at such a level! Fabian Osten-Saken was not a mere divisional commander, after all.