This question already has an answer here:
As we all know, if you want to make somebody aware of an response to a comment, you have to address them using
@username if it's not their answer or question you're commenting in. (Sadly - Facebook style notification of all participants in a thread would be way better. But that's a different story.)
If you forget to do this, and edit your comment to add
@username a short time later, will the user see the comment on their "recent" page? Or do you have to remove and rewrite the comment to trigger the notification?