We know for sure that even later in the Block 5 generation the re-usability got better. So that isn't controversial. I would assume their 'favorites' are being

We know for sure that even later in the Block 5 generation the re-usability got better. So that isn't controversial. I would assume their 'favorites' are being pushed in order to get engineering information on those flights, not because they are superior to the others of the same build.