Some Polish last names are gender-specific, at least in Poland. For example, while still in Poland, a male's last name would be Michalski, but his sister would be Michalska. However, this practice was largely dropped in the United States, so if those same individuals emigrated to the US, their US records would both be under the name "Michalski."
It would make sense that those individuals who lived and died in Poland would use the name as written there. Those individuals who lived and died in the US would use the name as written in the US. But what about the individuals who were born in Poland and died in the US? In addition, what about the individuals whose birth and death information is unknown?