This paper investigates the consequences of divergence in policy assumptions in energy planning for preparing national low-carbon pathways and enhancement of Nationally Determined Contributions (NDCs) in Indonesia, Thailand and Vietnam. We present an assessment of the resulting forecasts based on a multimethod exploratory study. Our analysis contributes to an ongoing debate on the policy coherence and integration in the energy sector and climate action strategies. Our results indicate how data availability, ownership and transparency, as well as institutional factors inbuilt in national energy planning impact policy implementation and climate action. This analysis can provide valuable insights for policy-makers working with enhancing NDCs to ensure the updated NDC is actionable.