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If you have sold these devices, you should delete them so the new owner can register them with his/her Apple ID. To do it, open http://supportprofile.apple.com, log in with your Apple ID, select Edit Products and delete the devices that you don't own.
If you keep these devices, you don't need to delete them, but if you want, you can do that
Do I need to do something about all the devices that are registered to my Apple ID that I don't own anymore?