Polish citizenship by descent - Great-grandfather left after the 1920 citizenship law but before 1921 census?

I emailed Lexmotion and said that they most likely cannot help.

I know that his birth records are in the archives in Ostrowiec, I've had confirmation of this. He arrived in the US in 1921 and my grandfather was born 2 or so months after they arrived. My great-grandfather didn't complete his military service in Poland, and was naturalized around 1927, but as far as I understand, because my grandfather turned 18 before my great-grandfather aged out of obligatory military service, he didn't lose his Polish citizenship.

The issue is they told me that because my great-grandfather emigrated before the 1921 census, it will be impossible to prove that he is a citizen. Is this really the case?

Thank you!

If it matters, he also seems to have lived in Osiek

@UraniumFever
Hello :) What year was your great-grandfather born?

It may be a matter of eligibility (according to the Polish law), not the lack of population census.