I am trying to figure out how to interpret cards that have this saying.

Say you are running a TIE Advanced with Advanced Targetting Computer and hit with 2 crits for your primary weapon. Would ATC then add a third crit? A similar question is for Kir Kanos, does his ability allow you to add another hit over and above the number of dice you rolled?

Indeed, that's exactly what it does. Just because you roll two attack dice, doesn't mean that's the limit on results. And ATC does exactly what is says - adds 1 <kaboom> result to your roll. The same logic goes for evade tokens - they add an evade result to your roll. So anything that says it adds to your roll, does just that. It's additional to whatever you rolled.

Core Rulebook, Page 12:

Add: Some effects add a specific result to the combat. To resolve this, the player places a token or unused die displaying this result into the common area.

Core Rulebook, Page 12:

Add: Some effects add a specific result to the combat. To resolve this, the player places a token or unused die displaying this result into the common area.

Awesome, I must have missed that. So that makes Kir Kanos and interesting choice for a sniping interceptor. And the ATC as a no brainer for the Advanced lol