An issue in the duplicated approach is keeping track of the different blocks once they diverge enough. In the best case scenario they all slighty change over t

An issue in the duplicated approach is keeping track of the different blocks once they diverge enough. In the best case scenario they all slighty change over time without forcing complexity on each other. But it becomes a problem as changes that should be breaking only break part of the code, and the rest can go unfixed as nobody remembers all the linked bits. It would be critical for instance if the duplicated bits were involved in invoicing procedures, and one in five remained unchanged while the other got updated.