You wrote:
“There have always been a lot of Poles living in Germany, who keep Polish names, but who are thoroughly German.”
That has been the case only since WWII. But since the 15th and 16th centuries there have been Germans with Polish sounding last names, however. You also used to find Old Prussians with Polish and German names. That was the case from the 13th century onward - especially among the junkers class of Prussia.
You forget the massive Polish immigration to the Ruhr area in the late 19th century during Germany's industrialization. Lots of people living in that area (and others) today have Polish sounding names. Give it up, your first post was utterly foolish/pointless.