Legal rights in unregistered but duly notarized POA, Sale Agreement?

No, unregistered sale agreement, notarized poa,will and affidavit does not confer title over property.

As per your facts if you have partly performed the agreement and further willing to perform or is in possession of the said property your legal right is protected vide S. 53A of the TP Act. In case you are not in possession then you can sue for specific performance to execute the unregistered sale agreement for protecting your legal right. Please refer the Hon'ble Delhi High Courts judgement in Rishi Raj Vs. Rakesh Yadav.

But for claiming a good title you need to register your deed of conveyance.

You have not posted the material facts.

Well analysed, opined and advised by experts Mr. Bartesh Goyal and Mr. Pradipta Nath, I endorse it.

Even if the agreement to sell is registered (not to speak of unregistered or notarised) it do not confer title over the vendee (buyer) for which conveyance deed / sale deed has to be registered with area Sub-Registrar.

Possession is another part of the transaction.

It would be better to consult and engage a local prudent lawyer for appreciation of facts/ documents, professional advise and necessary proceeding.