My view is that iteration of the core design is equally important to the the iteration that's done on the rest of it. The difference is that each 'product' in a

My view is that iteration of the core design is equally important to the the iteration that's done on the rest of it. The difference is that each 'product' in a field is a new iteration on the core design. This is what makes experienced engineers so valuable over inexperienced ones - the experienced ones know the history and know the previous iterations so that they can make the 'right' next step.