Balls pocketed on a safety are illegally pocketed balls.
Always have been. Always will be.
It annoys me that most rule books don't explicitly say this. Would really clear up the confusion.
Illegally pocketed? In leagues that count balls made, if you make your own ball on a safe it still counts as a point for you. And of course it’s very common in (league or amateur) 8-ball to make an opponent’s ball on a safety, like when one is blocking a pocket. Is that an illegally pocketed ball? “Illegally pocketed” sounds like a foul.