The relevance of energy in the growth and development process necessitates giving serious attention to the planning, production and consumption of energy. Energy modelling carried out in recent years using sophisticated and computerized models has become an important tool in planning and analysis of energy systems. These models rely heavily on future assumptions regarding the expected economic conditions in consideration to the current and unfolding situations of the economies in question. However, due to uncertainty of the future economic conditions, informality of especially developing economies and too much reliance on technical expertise of development/collaboration partners, these assumptions are mostly not well formed, hence found untenable to adequately capture the evolving events. This is more evident if one looks at the alternative energy projections made by different organizations using different understandings and assumptions. This study compares the best energy demand and supply projections of NECAL2050 as the best and most recent energy model in Nigeria with other alternatives projections and previous Energy Commission of Nigeria - ECN’s model to showcase the discrepancies and their economic consequences. It is found that in most cases of energy planning collaboration, modeling assumptions do not well capture the current and future economic realities of the assisted nations, resulting in misleading projections. Policy implications and recommendations are discussed at the end.