You saw those too.
I only have a guess but I'd say the sequence is wrong. Maybe it should be D/Q,R,S. It's alphebetical. Could be who they were manufactured for. Each company could claim they had the best price and defy anyone to beat them. I really don't know. Could be Quiet, Radical and Smooth.
I think it's who they were made for. The make shafts for other brands.