the notification shows up after someone else has replied to the topic, if no one else has replyed to the topic and your post is the last one when you edit it you wont get the message.
4.2.8: Editing Posts
Editing posts allows you to go back and fix errors, remove incorrect information, or add new information to your posts. To edit a post, look at the top right corner of your post and click Edit. You will be taken to the posting form to edit your post, and then click Submit to enter it into the database. If you edit a post after it has been replied to, a small message will appear at the bottom of it indicating how many times it has been edited, and when and by whom the last edit occurred.