I carefully studied this script today between patients and during my tea break... one thing became apparent: the order in which you call CSB and create your materials is important - this is looking beyond your CSBSurface(item) function.
This:
skinAndPaint = skin.mix(...)
uses this object:
skin = CSB(...)
Indeed, the order of creation of all of those materials has considerable significance.

I had a ton of questions today as I was reading - lots of questions answered, too! - but by the time I got home tonight and had my daughter's over-cooked pasta (her heart's in the right place - she just doesn't get the concept of al dente) my brain had turned to mush.

So, tomorrow, I'm going to try to implement this... proof's in the pudding. Those questions will most likely resurrect then...

Monterey/Mint21.x/Win10 - Blender3.x - PP11.3(cm) - Musescore3.6.2

Wir sind gewohnt, daß die Menschen verhöhnen was sie nicht verstehen
[it is clear that humans have contempt for that which they do not understand] 

Metaphor of Chooks