Vern's Volvo, or Vern's scrap heap, depending on how you look at it...

While the heap of parts all originally comprised Vern’s Volvo, they are not his car. Once removed from the whole, each individual piece lost its place as part of Vern’s car. Each time he had a piece replaced, Vern gave up that piece and made he new piece a part of his Volvo. He took ownership of the new pieces, and made them a part of his everyday life.
The new pieces are the ones that travel with Vern, that are used by him on a daily basis, and that do the work of the car. His car is the one that he has been driving for the past 20 years. The reason that the original pieces no longer comprise Vern’s Volvo is that the car is constantly evolving; the car changes and supposedly improves with each new piece, and the discarded piece, once replaced, is no longer a part of the working vehicle.
This could be compared to a team or group within a workforce: when a member of the team no longer carries out his or her job efficiently, he/she is removed from the team and replaced with a better, possibly younger worker. Despite the fact that the old pieces are all in one place, they are unused, and are no longer part of a whole, working machine; this renders them veritably useless in their current state.
In short: the old parts may have the potential to be a Volvo, but since they are not working as members of the team that is Vern’s car, they are sadly not Vern’s Volvo.