Filing for refunds for non-current previous years

Dear friends:

I ask this question with regards to efiling for non-residents holding E&O type accounts in India and deriving interest on the same annually.

01. Apart from the current previous year (2019-2020) how may years backlog can i file refunds for?

02. What, if any, will be the charges or penalty for late filing for REFUNDS (I can then balance the refund vs the penalty and decide whether it is worth the effort!)

03.  Do we use the same forms at the efiling site and fill in our resident status or is there a separate set of forms?

Thank you folks at CACLUBINDIA