How do you know?
 

How do you know what abilities are "rare." I have several blue officers I'd like to use to train up other officers, but I have no idea what their supposedly special skill is? Is it the level, like "Viral Matrix III," that make them rare... or is it the skill itself.

Look at the powers trainer in the space station. If you dont see a power listed there in the same rank your "Rare" BO has it then that is a 'special' power.

I have one BO who has a Rank 3 skill that is available to a rank 3 BO, but he has it in a rank 2 spot, which normally you cant do.

I havent yet seen a skill that is completely unavailable to be trained though. Just ones that are in different rank positions.