Kuromatsu (JBP) mame in the "wrong" soil

So I got this small Japanese Black Pine mame as a birthday present.
The little tree has a pedigree: misho from the hands of the japanese master Osamu Hidaka ( pt.wikipedia.org/wiki/Osamu_Hidaka ), he kept it for 8 years; sold to Regina Suzuki, who kept it for another 7 years; sold to Wagner Ribeiro who kept it for 3 years.
Now I have it.
It seems very happy in its organic soil that many people would call "muck". Some moss, signs of Osmocote® , I will work on reducing the size of the needles, and giving it a better form on the months to come.
But...
I will not repot it just because the soil is not the same as modern bonsaists say it is the only possibility.
The reasoning is: if it has lived and thrived for 18 years in this soil, why is it so bad for this bonsai?
And I found no answer so far.

By the way, sorry for the cell picture, not the best.

Nice present. What is the size of this? It looks like mame to me.

Krištof wrote: It looks like mame to me.

it IS a mame!
I thought it was in the subject of this post...:woohoo:
As for the size...

sorry I am going blind as my shift is coming to a close and I spent day staring at the monitor ....
So since it is mame my biggest concern wouldn´t be organic soil but the state of the roots, when it was last repotted.
Even though I use pure zeolite for my plants, I add something to hold moisture longer in such a small pots.
Last time coconut fibres to my mame ficus.

Krištof wrote: Last time coconut fibres to my mame ficus.

Good tip!
Plenty of coconut fibers here in Brazil, you can bet!

I would guess
Great stuff for airlayering too.
All right, good luck with the tree, I am curious where you will go with this one.