Can you elaborate what geographically you mean with Western Pollacks?
The initial most Western Pollacks are in the Poznan area. They are indigenous to there. And in the reddish area in this map
which belongs to the German Empire there were no Pollacks at all before 1945 (except for Upper Silesia). The whole Polish poulation in the even more western reddish territories is new and stems to a notable proportion from the so called Kresy, which is what Interwar Poland lost in the East, and arbitrary other parts of Poland. So dealing for centuries with Germans can just have been in the Poznan area (or corridor area, but that is likely not considered western now).
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