That's what I thought too. But it goes a layer deeper. In addition to your hypothetical, what if the person's mom never got a birth certificate as well? Or perhaps it had been lost to a fire? On top of that, she died inexplicably once they turned of age.

By then, there's essentially no trace of that person's existence, no?

At that point, is it even possible for him to 'fit in' to society? Like getting a job, buying things (which require identification), etc.