Gregory's Server
If you edit a post on Mastodon to add a mention of someone's account, they won't get a notification about it. If you want someone to notice your post, either mention them in the very first version of the post, or mention them in a reply and tell them to read the post you're replying to.
They also probably won't be able to see a mentions-only post if you edit their mention in afterwards (but do not rely on this as a method of hiding them from discussions of their account).