I note that it is recommended to use, say, a DMT 325 to lap a finer grit hone so as to eliminate any non-flatness. But why doesn't this then ruin the finer stone's finish? Is it that there are now coarse grooves worn into the finer stone but they don't matter because the blade rides above them, only contacting the fine grit surface, the void space that now exists in the fine hone simply existing and not doing any good but also not doing any harm? And over multiple passes the entire blade surface gets to contact the finer stone material?

That's the only thing that seems to make sense to me but perhaps I'm missing something.