RE: Transferring Control up an Existing 21 story building

Thinking like a builder rather than a surveyor, why would you need to carry the grids through the building if the shell is already there? I could understand the need for a new build with structural elements but since that's not the case, wouldn't resecting of the building walls/corners work? You're essentially trying to fit everything into the existing floorspace and with the building moving around as you get higher, sticking to the same control network seems counterproductive.?ÿ