I have to admit I committed that sin. Mea culpa.

My nakayama stone is only 14 mm thick. This is what kept the price below 4 figures. The bottom is very rough, and nakayamas are very hard. It would take ages to lap it flat.

I asked So what I should do, and he told me that sometimes a stone is lapped at the bottom to save the Kanji, but he told me he doesn't usually bother, and that there are no guarantees that the bottom is of as good a quality as the top.
These stones are hewn free from surrounding rock, and if the material against the bottom side would have been as good as the top side, than they wouldn't have cut it at that point, but they would have made a thicker stone (does my explanation make sense?).

After carefully considering my options, I took my DMT8C to the top of the stone and lapped it flat, destroying the kanji. I felt a pang of regret, but not more than that.
There is 1 kanji left on the side, identifying the hone, but that will be gone too once I laquer it.
I still have detailed pics of the kanji, to be included with the stone in the unlikely event I am ever to sell it.

But I really bought this stone for using it, not for looking at it or with the idea of improving my collection. If I ever want to get rid of this stone I can send it back to So, no problem. Not all stones he offered had Kanji on them, and the price didn't depend on them. There were unmarked stones that had nearly the same price per gram.

Btw I lapped the Kanji off my narutaki stone as well because lapping the bottom for the same reasons.