Prior studies recognise the enabling power of incompleteness in the design of Performance Measurement Systems (PMS). We add to these studies by exploring the ‘time dimension’ of incompleteness as a way to delve into the generative power of design. To this aim, we rely upon the experience of a knowledge-intensive organization during the design of a new PMS. While knowledge complexity engaged the participants within an open-ended design process, incomplete measures were associated with unfolding memories of the past and confident beliefs in future solutions, which generated effects through the knowledge gaps that they entailed, as well as through the projections in the past and in the future that they enabled. By delving into the time dimension of incompleteness, we add to prior studies on PMS design by showing the relationships between managers’ hopes for the future, patterns of memory (and forgetting) of the past and incompleteness in design. In particular, we show that although incomplete measures stimulate managers’ aspirations and search for further possibilities, it is forgetting about the past (its evolving memories) that triggers this search, facilitates new actors entering the design process and enables unpredictable outcomes of design.