Yes, this is correct, I have figured it out and have it working.
I realised that searching for a part that is a sub-component does not bring up it's Quantity Attribute (which was why my question was raised).
However searching for a main/top level part also brings up the structure of sub-component parts and their attributes including Quantity values. This works for me as I can see the quantity values this way.
I assume Navigate's View Part Structure tile is not designed to show all attributes when searching sub-component parts directly.?