While it is not a simple process, I have actually tracked down and found that “long-lost” car for people.
For the past 30 years, I have worked as a private investigator. Doing this work has taught me to be inquisitive, to look at a situation from many different viewpoints, to strive to find the answer, no matter how elusive. A large portion of my work has been finding missing persons. Primarily this work is done by searching and sorting through numerous database and resources. Since people own cars, these extensive databases and resources enhance my ability to find missing cars.
Knowing the provenance of a particular car can not only add significantly to its value, it can add interest to the car to make it more appealing to buyers. People love a story! Tracking down family members of previous owners is a rich source of information.