It is widely accepted that the way the interfaces between subsystems are designed is a major aspect of system architecture. The task of designing interfaces is made difficult by the technical diversity of subsystems, of interfaces, of functional requirements and integration constraints. Change management processes have long been implemented by the industry to monitor and control interface design. In this paper, change request data from several projects completed by Naval Group is analyzed. The Change Generation Index is introduced and a heuristic formula is proposed to link the maturity of interface design with change request generation. A promising parallel is established between the design process of a large system and learning processes well known to the social sciences community.