As several questions have brought up before, a long time ago, when a question was closed as a duplicate, instead of adding the duplicate link into the close banner (the one in blue), the Community user would edit the duplicate link into the actual question. Today, the banner of questions closed this way looks a bit confusing:
This answer to one of the questions bringing this up states that fixing this would be very difficult, since according to that answer the database doesn't reference the duplicate.
I suggested that maybe it would be possible to create a script that would check the revision history for the revision in which the Community user edited in the duplicate link, and from that link add the duplicate's ID to the database. The moderator who posted the answer suggested that I write the script, so as a first step in doing that I started writing a query in the data explorer that would find duplicates that didn't have a duplicate link in the database.
When I tried to do this, I noticed that despite what the answer says, the database does actually reference the duplicate. For example, this question has the problem in question, which is that there is no duplicate link in the blue banner, but if you search for it in the data explorer, you will see that the database has a field connecting this post's ID (18584) to the duplicate's post ID (9).
So apparently the references to the duplicates are there in the database, but for some reason the script that renders the blue banner doesn't use them. Could the staff look into exactly why this is, and try to fix it so that the duplicate link is present in the blue banner just like for any duplicate? Fixing it shouldn't be too complicated, I wrote a query in the data explorer that does that, so it should just be a matter of using a similar query in the script that renders the page.
This answer which is yet another of many posts bringing up this issue was marked as status-bydesign by an employee so I don't have much hope in this getting fixed, but I still think that the duplicate link should be added to the blue banner, even if it means that initially the duplicate link would exist both in the blue banner and in the post body.
If you do this, it will be easier to clean these questions up, because then all that needs to be done is that some user >2k reputation edits out the old duplicate link from the body as soon as they see a question like this, whereas if you leave it the way it is the duplicate link will also need to be edited into the blue banner which requires a moderator or a gold tag badge holder to do it.
