I heard back from my sister. She said it did happen a lot, but many times they would convert, so as to hide the identity. When she was in Warsaw a couple of years ago, she spoke with a researcher on survivors. So, my sister showed her a picture of my mom. The woman swore she must have come from the Ghetto, but my mom had to do whatever she had to do to survive. So my mom enrolled in a convent in Warsaw. It was the famous language school one. Being half Catholic, she might possibly pass. About my grandmother, it is interesting he lists himself as married, because we know for a fact that my grandmother died in an air raid. My mom tried to save her, but couldn't. If they did indeed connect, she would have told him that. Another mystery. My grandmother could have been half Jewish also, but still considered Jewish enough for the Nazis. I think they were known as "hybrids". Many converted to Christianity for safety's sake.