Nothing is yours until you accept the delivery of the vehicle, so the only thing you would be out is the deposit if you don't take the car when it's ready. Then again... once they are able to sell the car to someone else... they should give you back your deposit (That's how it works).
Now if that someone else happens to be you at a later date taking the car on a different promotion... then the process listed above works the same way.
So in short... YES you should always get the better rate until you accept delivery of the car.