Great question! We only use the fruiting body of all our mushrooms asides from Chaga.
With Chaga, it's a little bit more tricky. A yes and no answer.
First of all, Chaga is not technically a mushroom, it's a Sclerotia. Second of all, the Chaga fruiting body is actually not the most potent part of the mushroom and is very difficult to cultivate. For that reason, nearly all Chaga extracts are primarily extracted from the mycelium.
However, for that same reason, the mycelium of the Chaga is often referred to as the fruiting body. We know... confusing right?
In short, we use only the fruiting of our mushrooms asides from the mushroom that is not really a mushroom nor has a proper fruiting body. Hope that clarified and simplified things...