Realex uses Refunds for transactions that are more than 60 days. This will allow you to refund a credit card that is not attached to the original transaction. Rebates will have the original Transaction and the Auth ID and would only be available for transactions up till 60 days. After 60 days you would need to issue a Refund.
Note: Rebates are available in 4.92 or later. If you receive an error stating missing required field "Auth ID" you want to update your Chargent Package