Just because you stuff new stuff inside doesn't change the fact that the
airframe is xx-years old.
Last I checked, an xx-year old airframe doesn't have the same value as
one fresh out of the factory.
Likewise, the value of the new stuff stuffed inside the xx-year old
airframe won't have the same value as the same stuff in a box on the
shops shelf.
Once installed, it becomes used equipment and is devalued accordingly.