When Germans were expelled from Eastern Germany, there were some territories, where the contemporary "Tomenables" considered the population to be of basically full Slavic origin. Such areas were Upper Silesia, Masuria and easternmost part of Hinterpommern. People were then given the possibility to declare themselves Poles (I don't know the exact content of that declaration) and then they could keep their possessions and stay. All other were robbed everything and expelled. So you may consider how much such declarations reflected the real opinon of people or where motivated by something else.
The figures mentioned by Tomenable are from 1950 and he told me that most of these few "autochtons" in Pomerania later left for Western Germany. He will likely confirm this. Maybe they just wanted to have the possibility to at least sell their property instead of getting completely robbed. Even the ethnic Slavic Slovincians/Leba-Kashubs later essentially all left for Western Germany. This is why Tomenable has problems seeing these people from the village of Klucken for testing.
It's weird that Tomenable is so much advocating for all this "surpressed" by Germans indigenous Slavs being Poles, while these deeply rooted Slavs themselves in fact even left their homeland to escape from Polish rule. They survived abt. 800 years within the HRE/German Empire (since 1180 AD), but not Polish rule.

