Sorry for the very late reply on this post - I have only just joined the forum.
Firstly an introduction - My name is David and I work for GM, and among other things I implemented the CNC machine, design the cricket bats and produce the programmes for the CNC machine.
Grading - GM initially grade on how the blade looks (so grain structure and cleanness of the blade). After that bats will only be down graded on performance during production.
404 - Is our entry level unpainted bat and there is a little variation in grading as you described. Typically these bats will be wide grained, but occasionally in clefts you get something called a butterfly stain, and if a blade contains one of these stains it is automatically a 404, regardless of the grain structure, hence you can get a 404 with 10 grains.
Weight - As willow is a natural product you will always get a variance in weight, and this is the only thing that we as a company can not control. Our CNC machine allows us to make all Luna's to the exact specification- but they will however come in a variety of different weights depending on the density of each cleft. interestingly - you can get two bats with exactly the same scale weight but 'feel' different when you pick them up. This is related not only to the design of the bat, but also the relationship between handle and blade weight.
I hope this answers your question, and I am looking forward to becoming a valued member (hopefully!!) of the forum.
David