Sorry for the delay, I was wondering about that question as well and wanted to look into the relevant code before answering.
Edits to a post by its author do not trigger the same type of notification. So you might get a second notification for a post if it is of a different type, for example, userA replies to you, you get a notification of type “reply”, then userA edits the post and mentions you, then you will get notification 2 of type “mention”. This is the case even if the excerpt of the notification is identical in both notifications, we should probably not trigger a notification in this last case (when excerpt is identical).