Let's take a random automotive manufacturer.
It will normally go like this:
- Design of car
- Engineering
- Matching Design and Engineering and making compromises
- Developing parts and dependencies
- Start checking for space conflicts in 3D with other parts
- Start developing special tools - again with available space for assembly in mind
Once this is done, car will enter a slow manual build up process, where maybe 10-20 cars are being built, slowly, in a specialised factory by hand.
This is to make sure the dependencies fit, tools work etc.. During this process, tools and assembly steps are verified, put in order etc..
These cars will run first road tests, those are the ones you often see with some fake headlights etc....
After that, you bring the car to the plant and send the first pre-runners down the line. Those cars are almost series level of development (so all parts on that will go onto customer cars. Those cars will be used for extended testing, crash testing etc.....Normally, I'd expect a manufacturer to run at least two, normally three phases of these cars, during each phase shift new engineering solutions/part levels etc will be introduced based on previous experiences. Let's say the center console has a rattle in Pre-phase 1, so they change the clips for Pre-phase 2 and verify again.
The last phase cars are on customer level, these cars are also used for press events, motor shows etc.
Now since the cars from last phase are de facto customer level cars, but built before start of official production, you CAN upgrade them to customer spec (mainly software or removal of diagnostics). This is perfectly fine, UNLESS you just sell them to customers without doing that.
But what manufacturer would
DO THAT