Of course, a DNA examination is pretty darned good evidence of parentage or lack of but that doesn't mean you are taking your assumed parentage as a given with no evidence whatsoever.
I just had some 73+ year old 16mm films converted to DVD. It is darned hard to figure out the various relatives in the films with the meagre notes I have (and my parents very spotty memory) but I can tell which one is my Dad at 16 years of age. He is me! Dammed close to a clone.
I think that is not bad evidence that he is probably my father. That and the fact with age I become about as cantankerous as he.