1. An Agreement can be of "ANY" date (irrespective of it being of a restrospective date). Such agreement can be "freshly" stamped at current date, after paying the relevant applicable penalty.
2. An agreement necessarily is between atleast two parties and both the parties should mutually consent to payment of stamp-duty + penalty as on date.
NOTE: An agreement which is not stamp-duty paid or registered is still valid enough under the Contract Act.
Keep Smiling .... Hemant Agarwal