Nice review of your Karasu Harald-san.
Two comments about your review:
1. There is rumor that some sellers just stamp Nakayama and there are fake Nakayama stones in the market.
But I have another view of it.
About 10 years ago carpenters of kezukro-kai found that hard and fine Nakayama are best to their planes wich they use for competition.
Here some pictures of the competition:
Many carpenters bought Nakayama stones which give a keen edge on their planes.
Price of Nakayama stones went up and the quality of the remained stones went down.
Only the hype that Nakayama stones are good remained.
I think the Nakayama stones which are sold now are real Nakayama stones but just left over of the very good stones.
I think you could find a very good Nakayama because it was thin.
I write about thin stones in the next comment.
2. About thin stones
Many Jnats stone collectors with experience in Japan are looking for thin stones.
Not because thinner stones are cheaper.
The chance you find a gem stone is bigger.
The logic is that smaller sediment will take longer time to grow.
If you know about terminal velocity you will know that settling velocity goes down when the particle is smaller.
So the layer of very fine stones are thinner.