Is there a way to know which of my flags were marked as invalid?
Generally speaking, when a moderator takes an action on a post, the flag is dismissed as "valid". So theoretically if you don't see this:
then it could have been dismissed as "invalid".
However, there have been some interesting flagging issues of late. I think we should have a clear "Flag dismissed as ___" comment on each flag. How can we find out whether we've been flagging appropriately if there's no way to tell?