[drablyechoes]

There is more than one way to construct a synthetic identity, but in most cases that I've been aware of, a stolen SSN is used to construct the totally fake identity.

Using a completely fake SSN instead of a stolen SSN is what distinguishes "synthetic identity theft" from "synthetic identity fraud".

The identities in both cases are completely fake, but only in the identity theft case is the synthetic identity backstopped by a legitimate SSN that belongs to a real person somewhere. If that real person is a child or "off the grid", then the CRAs have no idea who the real person is and their SSN is ripe for creating a synthetic identity that will probably go undetected for years.