I'm trying my hand at figuring out similarities between Arnold and Karma in terms of AOVs/Render Vars.

There seems to be some distinct differences for LPEs like for example Karma using G(Glossy) instead of S like a lot of the other render engines do but overall one would hope that they somewhat match in behavior.

Currently I'm stuck at sheen.
It seems like Arnold and MaterialX has a concept of sheen in their shaders and in Arnold it's treated as part of the "specular" model and has it's own LPE that can be accessed with "C<RS'sheen'>.*".
But in karma it seems like sheen is treated as part of the diffuse calculation instead of it's own thing and I can't seem to access or isolate it like I can in Arnold.

For example coat works great and can be accessed with "C<RG.'coat'>.*"
but trying the same for sheen, "C<RG.'sheen'>.*.", gives me nothing.

Am I missing something here?
Has anyone played around with this before and could maybe guide me in the right direction?

Sheen might be a separable lobe in Karma, but probably doesn't have a label. You could submit an RFE to request for it be possible to isolate from the diffuse lobe.