These techniques are for people that do not want to be found. They purposefully hide and do not disclose where they live. They are either being sought for legal reasons or financial ones.
Cases such as these are treated and investigated the same way as a missing person in the first phase. Once those techniques have been exhausted, the investigations turns to conducting physical checks of addresses and making appropriate phone calls to try and find the person.
These cases are also evaluated prior to beginning the investigation and the client is given an estimate of initial cost and ongoing cost.