I think it's important not to be potentially provocative and use names like Pozen, Oppeln
No provocation intended. In genealogy, modern names are simply not that important. In 1918 for example, Posen and Oppeln were still part of the German Empire and their names as such "official", as you say. If you try to locate your ancestors in documents from that time frame, then you'll have to use the place names of that era.