The assessment of Common Cause Failures (CCF), i.e., failures of multiple components due to a shared root cause, is essential during probabilistic risk assessment in safety-critical industries. However, not all contributing causes to the CCF are directly observable at the component level as they typically stem from the systematic factors, i.e., design, operations, or environmental conditions. Thus, the industries need to implement methodologies such as the \(\beta \) -factor model to account for these causes. The \(\beta \) -factor estimation suggested by the functional safety standard IEC 61508 is based on the assessment of a defined set of defense measures. However, the extent to which these defense measures address the industry specific CCF remains unclear due to the limited contextual validation. In this paper, we evaluate the defense measures proposed by IEC 61508 with a specific focus on their applicability to the railway industry. To support this evaluation, we define a four-step process inspired by post-mortem analysis, a method traditionally used to learn from past projects. This process is applied to a set of historical railway safety events, allowing us to identify significant CCF events and their underlying root causes. We then make a categorization based on the root causes of CCF in relation to the defense measures outlined in IEC 61508 and estimate the corresponding \(\beta \) -factor for each category. Finally, we assess coverage and adequacy of the standard’s defenses in addressing the identified CCF. The insights gained from this study aim to support the development of more robust, context-aware CCF assessment methods for the railway sector.