As design and development progresses (typically defined phases per a plan), the level of rigor (including document control) increases. I am not sure the answer is as simple as above. For example, when are material specifications frozen so that they are in a condition to be approved and purchased for human use product? The approval of those specifications via an ECO process will occur during Design and Development. As you work on change control / ECO process, ensure that it complementary to your Design and Development for new products. As you think about ECO for released products, ensure the result of each ECO are records that maintain the Design History File (look out for Risk Mgmt) in real time. I agree that there are documents that do not require engineering change order rigor. Things like protocols, plans and reports can be simply approved and filed. HTH.