@larry I don't disagree with you here. It's a little like the story from the ship of Theseus: If you replace every part over time, at what point does it become a different ship? In my experience, if one is considering a rebuilt piano, then the quality of the technician who worked on the piano is at least as important as the name on the fallboard.
From what I understand, Steinway makes a big fuzz about repairs only being done with "original Steinway" parts - which is presumably a strategy that is just as much motivated by profits than it is about concern for old pianos. I recently heard a piano technician from my area bitching about Steinway buying parts like hammers or strings from standard companies (Renner,Abel,Kluge,...) and then reselling them for twice the price as "original Steinway".