370Z stock numbers
 

Hi everybody,
I tried to search the forum for this but couldn't find it. I apologize if already discussed.
All the online inventories I found, show the Stock NR along with the VIN, something like 12345. I've been told that if the number is pre-fixed with a D (ex: D12345) the car used to be a demonstration piece.
Are these codes standard and are there other codes/letters we should be aware of when buying a new vehicle?