Yes, you're reading it wrong.
Either way i try to read it, since there is no visible explanation next to the chart, "i am reading it wrong". Because in any case, Derby is sharper than Astra or if i read it the opposite way, sharper than Feather.
At any case, everyone is free to believe what he wants.
Derby Extra
(Green) 53 44 51 49
Astra
Superior Platinum 49 46 44 46
So, assuming that lower number is sharper, in shave 2, a Derby is sharper than Astra in shave 2. Then Derby becomes duller, slightly so.
Similar to Astra, which starts duller, gets sharper, sharper. So shave 3 is the sharpest in the Astra and overall they are very close to sharpness with Derby.
It's a theory...
EDIT: Wow, i noticed Kai blades are so similar to Derby! And to imagine that people claimed it's Feather-like!
EDIT 2: Also it seems almost all blades, are sharper after shave 3, than they were in shave 1. Amazing... I would have expected them to be duller.