I would off thought that if it was a bat for cook it would off been a higher grade like le but who knows because some off the bats that gray nicks try and pass off as le is quite scary and they are not cheap
I would imagine Cook goes to the factory once in a while, picks out a monstrous amount of clefts, GN make them into bats to his specs (Or various specs if he is looking for a slight change in shape), then he goes back and picks out 10/20 which he will keep for the season (Few test, T20, one day, Net/practice bats) and the rest go back into circulation where the GN batmakers reckon they can sell them.
No offence intended by this comment - but I would imagine, with the amount of heartwood, that this would have been a netting/practice bat for him (Something a bit harder wearing). I would imagine that 'Legend' would refer to the shape, not the standard of wood.
Can I ask what weight it is?
NB. I may add this bat reminds me of a bat Alex Hales had, which made its way to me recently. The bat looks very similar in looks but picks up and performs phenomenally well. Who knows really unless you speak to the batmaker