It goes without saying 40 is a small sample size. Yours just happened to be the largest collective I could think of off the top of my head. I've read comments here and there from others that also have a fair sized collection, most report a similar success rate. I've yet to encounter someone that had more than one or two stones they just couldn't work with. And when you do you have to wonder were the hones actually bad, or was there a component of user error?
Besides, if they weren't more hit than miss I imagine they would not have such a dedicated following and be viewed in the same light as a PHIG. Russian roulette with sharpening stones - one in 3 chance that it will be a great finisher, OK-ish 8K hone, or slow mid range hone shaped paperweight.