I do not know of a definition of delivery miles, pre-sale storage conditions may be important, I recall a country walk in Surrey nr Guildford and coming across around 40 new Austin Rovers cars stored in a Wood, Protected in factory wax but mud everywhere half way up the wheels, I lived near a VW distribution compound, workers would transfer brand new cars from a rail delivery point to the compound, workers were obviously on piece rates,new cars were driven flat out, workers would take a car home every night on trade plates, they would be driven flat out along the main road from the centre to the nearest town which mocked the running in of a new engine.
Some makers set the car mileometer to read a high number which rolls over to zero during a road test, I think it was Renault or BMEW