The EU Electricity Market Design reform requires transmission and distribution system operators to provide transparent information on the available grid capacity for new connections, commonly referred to as hosting capacity maps. These maps aim to inform the decision-making of new grid users, as well as renewable energy installers and flexibility service providers, thereby (safely and reliably) maximising grid utilisation and accelerating the energy transition. A key assumption influencing the available grid capacity is the definition of hosting capacity itself, of which currently no consensus seems to exist, both in academia and in practice. This paper examines five publicly available hosting capacity maps alongside relevant hosting capacity literature and identifies seven factors where different assumptions are applied to hosting capacity quantification. Furthermore, we qualitatively assess the potential impact of overlooking these factors in hosting capacity calculations (i.e., the tendency to over- or underestimate available grid capacity). In this way, we aim to contribute to the discussions on the harmonised definition and pan-European overview of grid hosting capacity, which are currently being developed under the EU Action Plan for Grids.