I think that if an inappropriate post was already resolved by a Community Sage - for example, a post getting archived because it discussed a topic that was resolved already, it should not be able to be flagged. Why? Well, here’s my case:
I accidentally posted something in a different category. After noticing, I immediately replied, saying that I posted it in the wrong category and that I request the post to be deleted/moved. 2 hours later, an CS actually went and archived the post. But a day after that, I got told that my post was flagged. I tried discussing that my post was already removed by a CS, but I only got (what I think was) a canned response which didn’t mention anything about how my post got already removed before being flagged.
So, I suggest locking the Flag option if a post has been archived. If a post is archived, it usually means that it had already been resolved by a Community Sage.
Well, maybe locking the Flag option entirely isn’t a good idea, but I haven’t thought about any other prevention of these cases.
So what’s the issue? Why shouldn’t we be able to flag after archiving? Don’t get me wrong, but flagging seems to be a solution to get rid your misplaced post.