Key persons can play an important role in the development and diffusion of new products, processes or technologies. Their functions, contributions and interactions within companies have been subject to numerous investigations. From a theoretical point of view, promotor theory focuses on several specialists to overcome different barriers to innovation, while champion theory concentrates on generalists playing multiple roles. Empirical results point to generalists being better suited for highly innovative projects, but on the other hand different roles should preferably be played by different key persons. A central gap in the literature is that this issue has not been investigated sufficiently so far in an inter-organizational context. The questions are: Is role accumulation beneficial for innovation project performance with respect to the key persons? Is role accumulation even more advantageous with increasing degrees of innovativeness? A sample of 107 innovation projects where small and medium-sized enterprises take part is used as a unit of analysis. The network manager served as the respondent. A measurement approach based on an extended Rasch scale was introduced for this purpose. The results show that indeed ‘too many cooks spoil the broth’: Instead of many single-role players in each organization, we need a few multiple role players in an inter-organizational context.