I think it might be a time based thing.
Like if you edit it in the first few mins after creating it, it won't leave a note that you edited it.
If you edit it some period after that, it leaves a note saying you edited and the timestamp.
And then after some longer period, the ability to edit at all goes away.
Or maybe I'm just totally making that up, but my brain told me that.
The only thing we have to fear, is fear itself. And bears.