Yea i was wondering about this too. I've seen a number of mobs that have been given surges or far more surges than they even have ability to use. Even double checked the rules to make sure it wasn't a case of being able to use abilities multiple times, but nope...
If I remember correctly, troll and sorcerers dont have skills to expend with surges, maybe adding one more line in the activation like expend two (or more) surges to add X damage, revolves the issue.
Ah ok, didn't realize they were from a pool. That makes a lot of sense now. I was worried i was missing something.