Originally Posted by peteropny

You read correctly - it used to be that status gets attached at reservation and not updated. Recent reports though seem to indicate that status is correctly reflected at checkin. So probably no need to call especially for run of the mill properties where Diamond gets you club access / breakfast since these can be added to any room. However, if your stay is at a property where Diamonds usually get a much better room than non Diamonds, it couldn't hurt to call.