Whiting introduced the Olympic grading system as a marketing strategy. As was said it has to do with the amount of usable feathers on the hide. Different breeders go for somewhat different effects. Whiting goes fro long thin stems. Collins goes for variegated thin stemmed hackle. The Hebert line varies from Whitings main line. IMO you cannot always get the look you are looking for from breeder. That is one of Whiting philosophy's.

I can tell you that there has been changes in the breeding over the last ten years. That is one reason you can not find good spade hackles any longer as they have been bred out.

I have stuff from the '70's through today and one can really see the difference.