it is possible that the car while going down the assembly line was destined for the original engine and was even fitted - but during the shakedown testing at the end of the line might have had a catastrophic failure and had to be fitted with a new engine - even though the car had not left the factory. OR if it was a very early one (0 series) the engine might have been replaced by ford to sell as as a new even though the car may have done a few miles under fords ownership as a development vehicle.