How embarrassing...
We've been playing since the Edge of the Empire Beginner's box came out, just upgrading characters as the rulebooks became accessible and so on.
One of the rules we've been playing with is that, when a particularly important Nemesis takes damage exceeding its Wound Threshold, after it suffers the Critical Injury, the GM may spend a Destiny Point to reduce the Nemesis' wounds to one below its Wound Threshold.
This gives important Nemesis a chance to escape and makes it possible to actually kill off the Nemesis via a high critical injury.
Since getting the Age of Rebellion rulebook, and now looking at the Force and Destiny Beta, I have not seen that rule. Am I imagining things? I can't remember where I read it, and I can't seem to find it in any of my books.