Will I get this refund immediately when I surrender my plates?
When you surrender your plates, your Receipt FS-6 T indicates if you are eligible to receive a refund.  If you are eligible and you do not request a transfer receipt, the refund will be processed automatically and you will receive it in the mail in several weeks.
What was the form that would indicate if I am eligible for the refund?
Your Receipt FS-6 T indicates if you are eligible to receive a refund.