Unused Slot for Deactivated Account

I bought Vituo/Dulce here recently, and during the reference acceptance process it came to my attention that he had an older ref! It was published in 2016 and appears to be the only other ref if I see it right. I'm not sure if I am missing any other refs.
Here is the old reference. The user's name was Aareniel. They have slot 4. I have no idea who this person is or if they changed accounts, but their slot is marked as unused. I'm not sure what to do with it. 

Also, searching the BDA account I see at least one has been born, but I don't know who used what slots, and none are marked on his plaque. Is there anything you can think of to help me confirm? 

I wasn't expecting a fun round of new info, ha! I think it's all okay, but I'm a little lost. Let me know what you can help with, thank you!

Hi!

The slot that belonged to Aareniel has been used, so it is unable to be removed. I did some digging and worked out the slots for you below, feel free to copy and paste if you'd like! <3

Username | Payment | Status | Mare | Foal
1. TSDTR | Old Ref | Used | ID 774 | ID 1246
2. TSDTR | Old Ref | Used | ID 600 | ID 1248
3. War-Colt | Old Ref | Unused |
4. Aareniel | Old Ref | Used | ID 1580 | ID 2020
5. MistTheElf | Old Ref | Used | ID 1565 | ID 2205
6. Sammieasmagpie | Old Ref | Unused | ID 1780 
7. 11IceDragon11 | Old Ref | Used | ID 1780 | ID 2252
8. Open
9. Open
10. Open

We have also added his foals to his plaque comments, thank you for bringing this to our attention! Some of his foals' plaques were not filled out, so they wouldn't show up in BDA when Vituo's ID was searched. In these situations I find the best thing to do is go to the original owner's profile and search the ID there to see if it brings up any old foal designs. You can also do this with the people who own the slots  

Apologies for the delayed response on this! We appreciate your patience and hope this helps!