Here is the relevant passage from Russell's Problems of Philosophy:"It will be seen that there are various stages in the removal from acquaintance with particulars: there is Bismarck to people who knew him; Bismarck to those who only know of him through history; the man with the iron mask; the longest-lived of men. These are progressively further removed from acquaintance with particulars; the first comes as near to acquaintance as is possible in regard to another person; in the second, we shall still be said to know 'who Bismarck was'; in the third, we do not know who was the man with the iron mask, though we can know many propositions about him which are not logically deducible from the fact that he wore an iron mask; in the fourth, finally, we know nothing beyond what is logically deducible from the definition of the man".
Russell gives examples in which he assumes various degrees of external (outside of the description) knowledge about the objects described, more or less based on colloquial understanding of these descriptions. If we change the assumptions on this score then of course his analysis will change accordingly. For instance, if we assume that we were able to survey all men that lived and identify "the longest-lived of men", let's say it was Adam, then we would be in a position to "know of him through history", and perhaps even attach biographical details based on the biblical account. Correspondingly, a person who knows little of history may well be in a position to infer nothing about "the first Chancellor of the German Empire" than what is forthcoming from the description itself.
In other words, while different people may use the same description, the scope of judgements that can be made based on this description depends on the knowledge of the person who is using the description, and is specific to that person. Moreover, it may expand as the person gains new knowledge, e.g. that the first Chancellor of the German Empire was one Otto von Bismarck, and gets acquainted with his biography. As Russell says, "knowledge concerning what is known by description is ultimately reducible to knowledge concerning what is known by acquaintance".