Since the Ghostwriter badge is for people who wrote topics that have been adopted as official documentation, you absolutely deserve to receive it. I’ll grant that to you now, for that post 
I’m going to look into a way to see if we can retroactively see which posts were previously written by community members before becoming official documentation. I know we could do it for individual posts, but to do that individually for 500+ posts is very time-consuming, so if there’s an automated solution for this then I will find and implement it.