So, I finally found and verified my great grandfather's tombstone. It is written in polish, but easily interpreted. Thanks to the tombstone, I was able to order his death certificate, which I received in the mail today.

Tombstone dates:
Birth = UR DNIA 24 CZER R1891 (24 June 1891)
Death = UM DNIA 18 LISTOP R1929 (18 November 1929)

Death certificate dates:
Birth = 11 October 1894
(based on his age transcription of 35 years, 1 month, 7 days)
Death = 18 November 1929

I was hoping for some insight on which is more accurate and why there is such a discrepancy. I assume the tombstone is the date to go with?

Thanks for your help!