land discrepancy catastral/land registry

Hi All

We have our house for sale and have some 500 more m2 on title deeds , land registry morecthan on catasrral. We were not bothered to correct as in our area 5000 needed for legal construction and both figures over 6000. However as we want to sell we have had Architect out to measure land. Typically neither the figure on Catastral or deeds correct though surprisingly the catastral is nearer.
Our question is , the Architect has submitted a report to rectify catastral and says this is sufficient and we can produce a copy for buyer if and when a buyer appears. The agent however believes we will need to have new title deeds. Notary etc.
Can you advise ? I thought new deeds always drawn up for new owner so it makes sense to me that it would be then that the amount of land is rectified