Western Prussia and Pomerania residents may have come from other parts of Germany. Depending on events in the various kingdoms, city-states and other regional events your relatives ‘may’ have come from a place in a non-unified Germany that you never thought. Don’t rule out that your ancestor may not be of original Prussian identification but maybe Saxony or other locations. I am trying to learn the patterns of migration within the various German Provinces prior to 1800 and after the Napoleon Wars ended in 1815.