My great grandmother was from a rural poor area. She only knew that she was born in the spring in "the year of the big flood" which neither she nor local recor

My great grandmother was from a rural poor area. She only knew that she was born in the spring in "the year of the big flood" which neither she nor local records could identify. When we brought her to city hall, the just asked us what birthday she wanted and she picked her favorite number in her favorite month in spring and we guessed a year which was probably +/- 2-3 years correct. Lots of bad data with lots of human bias.