A design rationale (DR) is a representation of the reasoning which has been invested in a design [1]. This short paper describes the use of the QOC Design Space Analysis approach to DR [2] to document the evolution of design concepts over the life of a three year project. The goal was the production of a retrospective DR document which filtered, integrated, and indexed discussions from a wide range of sources across the project. Designers’ reactions to DR in general, point towards what kind of DR is most needed in development teams, and how DR of different sorts can be integrated with existing forms of design document.