Even if it doesn't have the VIN on it, it is a production serial number that is tied to the customer order and the VIN. We use a different system here at BMW. There is a number we call the IGEF number, which is stamped into the body near the front shock towers. That identifies that body as it's being built and ties it to the customer's order. Then, when the body is assembled, it gets married to a temporary carrier that enables it to ride the conveyor system. The carrier has another number on it with a QR code that cameras can read. So, at various checkpoints through the paint shop, the cameras read that QR code which is tied to the IGEF. That's how the computers know what body style (model) it is and what color to paint it. This info is fed to each individual robot so it knows what program to run for the proper paint coverage and physical profile of the body (robot will crash into it if it runs the wrong profile) and, of course, what color paint to use. After painting, inspection and repairs, it goes to assembly and the carrier is removed. Then they just use the IGEF number to assemble it right. I'm not sure when the actual VIN is assigned.
Now you know more than you wanted.