It seems that design controls can be ever changing with how the device is developed over time. Reading over the previous replies, it is true that companies can not change the design controls forever. If that were the case then they would never create an end product.There must be a point where they decide that the device is safe enough or the most optimal parameters have been chosen where they do not notice that many changes within the medical device. They should be creating a device that can withstand subtle changes without causing other major issues.