I'm not sure what you mean. In this case the exploit did remain a secret until such time as a targeted individual was paranoid enough to send the link to an inv

I'm not sure what you mean. In this case the exploit did remain a secret until such time as a targeted individual was paranoid enough to send the link to an investigative team instead of clicking on it (and this is what resulted in the patch), or in other words, nobody else besides the attackers, the victim, the investigative team, and Apple knew about the exploit until the patch shipped.