This 'grandfathering' is how everything works these days. Literally.
Thirty or forty years ago when the Japanese were making reliable cars that were putting European and American stuff in the shade, people wanted to know how. The fact that it was copied from something was perceived as a negative but that was the secret. 80% proven technology and 20% new.
It doesn't matter whether it's aircraft, cars or mobile phones, the facelift model is actually half of the new model under market test without the new fancy bodywork and the new model is the facelift model with the barely consequential glitz added.
This is so ingrained in the engineering profession now that those of us who have real ideas and want to do something new are seen as weirdos.
