what he said.
when the cank is made and linnished its measured and given a grade. so when its assembled by the factory, they look at the grade numbers to get the desired oil clearance instead of re-measuring and so on.
graded bearings are only useful if using a BRAND NEW CRANK, then you can pick a grade to suit the size oil clearance you want. as far as im aware once the crank is linished all that goes out the window. (the grade numbers on the crank)
subaru do the same thing but with pistons aswell. each block has individual cylinder grades.