Ah, Grandfather's Axe - for the hard of thinking:
"Grandfather has had the same axe for forty years, it's had 6 replacement handles and 3 new heads, but it's still the same axe"
Things evolve as they are used, damaged, repaired, whatever - as long as there is a common traceable history linking the item back to the factory-produced original then it is the same item, in my view. How much of our bikes has been replaced since they left the production line? 5%? 10%? More?