All of the information available to family historians is the result of thousands of hours of work and even lifetimes of work. So what if the story that grandmother told isn't exactly accurate. She took the time to tell it and it may have a lot of good clues. Snobbery has no place in this world and especially not in history.
Mistakes are part of being human.
I would be so glad if someone had entered my brick wall into the IGI, even if it was incorrect at least it might give some clue. In researching my predominantly Irish Catholic ancestors, I have to occasionally remind myself that they weren't all Catholic. We have found several ancestors in Bishop Loughlin's Dispensations, Diocese of Brooklyn, 1859-66, Vol. I, by Joseph Silinonte. Until now, comparing databases with someone else has never been easy.