Law /
Citizenship by descent: don't know details of grandparents' American citizenship [8]
@dzef: yes, USCIS is a valuable means to determine the status of American citizenship if not in possession of a Certificate of Naturalization.
Be mindful of the fact this process can take 18 months to complete - this may be done simultaneously to Confirmation of Polish Citizenship.
Ironically, sometimes 'No Record Found' (or words to that effect) is your best outcome as this implies American citizenship was not obtained.
@delphiandomine: you are correct in that the Polish bureaucracy might seem as inefficient as any - including the American one (see above).
However, this is because Confirmation of Polish Citizenship is decided at the Regional (Wojewoda) Level of one's ancestor's known residence.
While I have not obviously addressed all nuances and caveats, my understanding of this process comes from my own successful Confirmation.
P.S. Again, I recommend a thorough read of the link I have provided. If needed, most attorneys are honest and reliable - I used one myself!