How did they manage to sue a school years later?

I would point to actual articles but I seem to not be finding many although I do know they were published in newspapers and the like.

I’m referring to people who attended private schools or schools of any other kind, only to end up suing them over certain things many, many years later. How the heck did they manage to be able to do that? Doesn’t that require a lot of evidence and how would it be possible to acquire the kind of evidence to sue a school for, e.g. neglect of the person as a child when he or she attended it (as it’s a school’s duty to ensure the wellbeing of the child when at the school).

I’m completely stumped as to how on earth they would ever have managed to pull that off, in one particular case it was some twelve years later and the ‘victim’ was in her 20s!