You could never even truly know if a "genuine" sandman still had its from the factory body shell. If it was T boned as it left the dealers it would have been repaired under insurance and if it needed a new shell or chassis it would have been replaced. It would have still retained its original numbers and plates. Now 30 plus years later and the current owner believes its a un-touched survivor. All hypothetical of course, but totally possible.
They are NOT works of art. They are simple old Holdens that any Joe Blow could modify in their back yard, and that IS what happens to them.