Standardization is the foundation of all large-scale production. Manufacturers produce separately many copies of every part of a complicated machine to use on an assembly line. Standardization also allowed owners of machines to order and replace any broken or lost parts, taking it for granted that the new part would fit easily and precisely into the place of the old.
Yes this really is the point. Regarding, for example, Nimrod
The legacy airframe components were difficult to integrate with the new build elements and they give an insight into just how bad the older generation aircraft were. There were differences of up to 4 inches in length between parts of the legacy fuselage components. By comparison, for the Boeing B777, which first flew 15 years ago, Boeing claim each aircraft to be within 3/100th of an inch of each other over a fuselage length of 200 feet.