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are there any elements to an LR argument stim other than: premise, sub-conclusion, conclusion?
i'm asking because some premises don't seem to be directly lending evidence to the conclusion; they just seem to provide context.

As you have noticed, not all arguments include information pertinent to the argument. This additional stuff is called "background information." The information doesn't directly relate to the argument(s) (if there is one), and can be viewed as information that's meant to trip you up.

(This is from the LRB)

there are also additional premises --these don't directly help anything, just provide icing on the cake and/or distract you.
and there are also counter-premises--contradictory premises that the author might discredit at some point of the stimulus to help strengthen his argument.