Good to hear someone else discount the 'if it floats it is not viable' theory.Soaking the seeds is a good way to get that process started in my experience. As of this morning only around 6 seeds have sunk from the batch yesterday, which to me indicated the water has penetrated. I'm not too surprised given how thick that shell is so I'll leave them to continue soaking longer.
I've seen a number of people reporting that floaters have germinated. I know that unviable seeds do float in water but some good seeds seem to have enough air inside the shell to make the seeds float so I'm confident that some seeds that float in water are still good. I sow all seeds. If they are not viable they won't germinate but at least I'm giving them all a chance. Maybe if you're sowing 1 seed per pit it would make sense to sort viable and unviable but the floating V sinking does not seem to be an accurate ID method.