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Nice looking stone... Ozukus can make very nice finishers... That looks like it's a surface inclusion and should lap out. You probably realize this but you're not done lapping at the point the second...

Post a photo of that JNat... a visible crack on the top doesn't sound good. If you can feel it with your fingertip, it will cause trouble when sharpening. A quality vendor will swap it out/replace it...