Every lease must be registered with the Agenzia delle Entrate. An unregistered contract is void against the tenant, which means the landlord loses the terms and keeps the obligations.
Cedolare secca lets a landlord swap progressive IRPEF for a flat substitute tax, at the cost of freezing ISTAT indexation for the term. On a long lease in an inflationary year that trade is not obviously good.
Possession runs through the court calendar, not the contract. Any Rome yield model that assumes a fast recovery of the property is a marketing document.