Question answered by reading other posts.

Can't find a clear answer in the rules so I ask here. Can enemies also use Cunning and Expertise as defense in combat?
Happy for any knowledge or thoughts about this!

Yes, but under same restrictions in terms of C for mental only, but an NPC can't spend more than one cunning die per roll.

So use them or lose them - an NPC going down with those unspent is weak sauce. On Observation etc. (them goblins with their cunning hear your coming because they sprinkled twigs you step on etc.). Remember to use them defensively too. Cunning for spellcasters or NPC's resisting a PC's mental skills of Intuition or other.