If a JIDS user account is deactivated at some point, whether by compact office request or due to a user clean-up as part of the performance measurement assessment, the user will no longer be listed on a state's User List in User Management.
In addition, because the account still technically exists in the database, but is hidden from your view, the compact office will be unable to re-add the user account. This is because the username is already taken as a unique account in the system.
If you are trying to add a user but the account is not showing up in your User List, it is likely because the account was previously active and therefore cannot be re-added. The user account can be reactivated by request of the compact office. This will restore the user's access to JIDS and will put the user back on your state's User List.