Are these additional to the current fleet?
Some of the earlier 'cabs' have been pretty hard used over the last few decades and I would have thought that the new aircraft, whilst sporting all sorts of new stuff and hence improved capability, will actually replace the original survivors.
The very early cabs went back to the US in about 1993 or so and have then been upgraded twice (?) since, so they are probably like the original broomstick which has just had three new shafts and four new brushes!
Old Duffer