C-Bert
Valid point re interfaces between the blocks. However, the PCO is unlikely to have sufficient manpower to do all detailed design for the four blocks plus all the hangar / gallery / FD blocks.
Each shipyard will also have particular preferences / limitations for building the blocks which is best done by those in the yard who know. Probably the best solution is to set hard interface datums at block boundaries (done by PCO), but let the individual yards sort the detail in block.