To find out what stairs you can currently challenge someone in, first go to the Main Stairs Page, then click on "Show your stairs only" link. The ones in BOLD are ones you can make a challenge in. .
Perhaps after a post has been deleted then the posts about the post can be deleted too. Then people won't write posts about the post about the post or post about posts that aren't the post. And there certainly won't be any call for posts about the posts about the posts.