Registration act 1908 and stamp act

Why was sale deed registered by sub registrar in 2018 when power of attorney has been cancelled in 1998? a sale deed was executed on behalf of Holder of Power of attorney in 1995 and presented for registration but sale deed didn't get registered due to difficiency of stamp and sent it to collector for further proceedings. In the meantime power of attorney was cancelled by principal of power of attorney. The order was passed by collector to pay stamp duty for registration in 2004. stamp duty was paid in 2017 and sale deed get registered in 2018. Now question is that the registration of sale deed is valid according to law because power of attorney has been cancelled by principal POA?