Process reference models can serve as a tool for simplifying process problem-solving during software development software. In the authors' research project, they developed a process reference model for software product line product derivation. The development was completed in four stages using sources in industry and academia. In this study, the authors discuss their research approach. They include an explanation on how the different stages of the research form a continuum in which the model is continually adjusted, and describe how empirical evidence was used in the development of the reference model through following an evolutionary multi-method research approach. Following a discussion on each research stage, the authors briefly present the evolution of the reference model they have developed, Pro-PD, as an exemplar of their approach. The study contributes to an improved understanding of real world reference model construction. Importantly, the authors also present lessons learned while implementing the approach. This research contributes to the practical implementation of reference model construction guidelines.