EDIT This question is about a general mechanism to draw attention to old questions that have received a new "close as duplicate" vote. It seems that the chances of an old duplicate question receiving extra attention are very low, and the only recourse is for the close voter to hang out on chats and ask for more close votes.
Below is just a specific example from StackOverflow.
I voted to close the duplicates 3 weeks ago. No activity (that I can see) occurred on the questions. I then flagged the questions for moderator attention, but my flag was declined:
I feel that I've done more than my part in signaling the duplicates by making a note to check back on those close votes three weeks later, and unfortunately I don't have time to canvass for votes on the chat. Is there a mechanism that takes over from here? I assume we want to continue encouraging volunteers to find and report duplicates.