I found this video very interesting when you posted B, ta. Do you have both?
I've only had Cerax 3Ks, not an Ouka. But from what I've read there have been people told by Suehiro (including people who sell them) that the stones were the same.
My suspicion is that your man has stones at different levels of 'worn in'. or soaking over time changes them, or something. There are probably a lot of variables at play - even things like exposure to temperature during the initial shipping possibly has the potential to affect a stone...
(I'm guessing whetstones aren't shipped air freight. Deep sea shipping takes a long time, and temp spikes can be extreme in containers at ports.)