[Graham Boak]

This isn't so - else there would have been no need for any change in designation. You can see similar differentiation on other types, for example the B-24H being limited to Ford production. Please be careful with the use of the term "interchangeable". This has a specific engineering meaning, where one piece can be simply transferred off one aircraft and onto another without any rework. "Plug and Play", if you like. Other replacement parts may look common but could not be fitted to the "wrong" airframe without rework. As appears to have been the case with these Fw190 tails.

You can certainly guarantee that the majority of the airframe parts on WW2 aircraft were not interchangeable, even from the same production line, because this costs time and money to achieve. Production lines committed to long runs of the same type will have more interchangeable items than lines run on shorter batch orders, because of the ability of justify investment in more extensive tooling.