On my flagging history on SO, I have the following spam flags numbers:
387 posts marked spam 377 deemed helpful 4 declined
I have no recent spam flags that have not been handled. By 'recent', I mean within the last few months. It seems unlikely that there could be very old spam flags that haven't been handled one way or another.
So, what happened to the other 6? Were they eaten by a hungry unicorn? Did something else happen to the posts which caused the flags not to be handled at all?