By reading and applying critical thinking in evaluating said material. Unless you are parroting the infamous FSB playbook of 'question everything it will muddies the truth'.

> How would you know if someone less famous got disappeared?

https://en.wikipedia.org/wiki/Russell%27s_teapot

Almost everyone living in the US has some sort of record. They went to school, had friends, teachers, family, etc.

It's unlikely you wouldn't know someone has disappeared, especially if they were important enough that the government decided to illegally disappear them.