First, when any new drive is placed in a K component (Server, Server-Players) the drive becomes part of that Server's system of drives. It does not matter whether or not that drive ever received content, it is still identified to the drive set in that Server. Subject to the exception discussed in #3 below, it cannot be removed, sold, and placed in a different device (Server) UNLESS it is first reinitialized by K, and this process requires returning the drive to K to have this done. Once a drive is reinitialized, it can then be placed in any Server/device capable of using that drive. Here are the other considerations:
K will only reinitialize drives that are still in warranty.
There is a fee for this service. It was $250 for the first 6 drives, and $30 per additional drive in the past, check with K Support for current fees.
This process is not required if ALL of the drives in a particular Server are being removed and placed in a different EMPTY Server. You cannot add the drive set to a Server containing other drives. This is important because some Seller's of drives have told potential buyers that as long as you are buying and installing all of their drives, you can place them in a Server that already has drives but has enough empty space to accommodate the used drives. This is incorrect.
So when shopping for used drives, be sure to confirm the drives have either been reinitialized by K, or understand that you need ALL of the drives that were in the Seller's Server and that you are placing the full set in an empty Server.
Additional note: Given the recent changes at K, it is possible that the ability to reinitialize drives may end at some point, or the fee structure may change.