About the only other think I can think of is this: beware the "screaming" in your voice. A truly experienced criminal is going to be able to gauge the extreme lack of motor control that may be indicated by gross inability to control your voice.
What I mean is this. Consider how deeply creepy, vile and evil the attacker's voice sounded when he quietly spoke his intentions to you. Stopped you cold, yeah? Had he spoke it just a bit louder and more forcefully, you might well have been frozen solid, like a rabbit in the headlights.
The point is, the voice can be a tremendous tool in such a situation. But it can also give away your ability to control yourself, and hence the likelihood of your being able to thwart an attack that proceeds irrespective of your just having drawn a gun.
One nice benefit of focused force-on-force "stress-induced" training can be the improved ability to control your voice in such times. Better physical control, better breathing, better voice modulation ... can equal better control over the situation, as you apply your best, concise, most "evil" voice in return, telling him exactly what's going to happen.
"STOP!!! DROP YOUR WEAPON ... or be eliminated. NOW!! DROP IT NOW!!" And if he doesn't, you need to realize he probably won't, and that his two supporting thugs are likely to get in gear to help him in the attack. Remember that a knife and deadly intention is within yards of you at this moment. No screwing around will help you. If he doesn't immediately react, then you put him down.
Again, you did fine. This time, this particular criminal wasn't as hard-core as he thought he was. He didn't detect the "screaming" in your voice that might have indicated inability to control your actions well enough to matter. Still, you drew the weapon, targeted your sights, made it clear what was about to occur. He left. Which is the best possible solution. Kudos.