I agree with Dani and will provide a true example. My paternal grandmother's headstone says that she was born on May 30, 1895. When we unveiled the headstone in 1983, my grandfather asked if my father approved of the birth date he chose. My grandfather explained that they had lied so much about the date that he didn't remember the truth so he decided to make her younger for eternity.
Many immigrants like my paternal grandmother had no documentation of their birth. She knew she was born in the spring so she chose May 30th, Decoration Day later called Memorial Day, because she wanted her birthday to always fall on a holiday. No one has any idea what the exact date was.
