Workload control (WLC) is a leading production planning and control (PPC) concept for manufacturing environments subjected to high levels of uncertainty, such as in the make-to-order (MTO) industry. Despite the importance of this concept, few case study applications of WLC have been presented in the literature. This paper takes advantage of a rare opportunity to explore two independent longitudinal empirical WLC projects recently undertaken in Portugal and the United Kingdom. Uniquely, the projects were conducted in parallel and both chose to incorporate the exact same influential WLC methodology in the development of a decision support system (DSS), thus providing an ideal platform for cross-case comparison. The paper focuses primarily on theoretical refinements which ultimately had to be made to the WLC methodology applied to the two cases. Reasons for the refinements can be broadly split into two groups: (1) refinements due to the time that has elapsed since the development of the original methodology; and (2) refinements due to company specific characteristics. The paper also reflects upon a number of implementation difficulties common to both case studies, providing insight into how these could be avoided in the future. Finally, eight future research challenges are presented.