Very nice discovery. And you're right, the former registration number is painted under the FNI 78 registration
The vehicle is a Renault KJ and here is the registration history.
9256-Z3 : issued in the Seine-et-Oise department at the beginning of July 1924 (maybe the first registration) 4089-YB7 : issued in the Seine-et-Oise department on 5 January 1937 8197 CE 78 : issed in the Seine-et-Oise department on 28 May 1955