1) What does the Sales Agreement say in case it is not followed by a registered sales deed within the period of two years ? Whay have you waited so long ?
2) If the Sales Agreement is silent on this aspect, you can void it while the Buyer could dispute it by trying to bring evidences to the contrary.
3) In any case, the sales deed since not registered shuld not result in transfer of property. The Buyer could have recourse to other alternative remedies in the meanwhile depending upon the exact Agreement terms and events subsequent.
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