Can I get a Polish passport?

Hello, this is a little complicated, but perhaps someone here can answer my question. My paternal grandparents are Polish, but lost their citizenship during the war, and have no documents to prove that they are Polish. My grandfather has since passed away, and the problem is that my grandmother was born in L'viv (Lwow) when it was part of Poland, which leads me to believe that it may be somewhat complicated to track down any of her records, if they even still exist. Would anybody here have a clue as to what I could do to acquire citizenship under these circumstances?

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