Concentrated solutions of short blunt-ended DNA duplexes at room temperature can form liquid crystal phases due to stacking interactions between duplex terminals which induce the aggregation of the duplexes into semi-flexible linear chains. Mesophases observed in these systems include nematic, columnar and cholesteric ones. This experimental system is just one of many examples, where liquid crystals ordering emerges as a result of molecular self-assembly into linear chains. In the attempt to go beyond a simple Onsager theoretical approach to understand the thermodynamic behavior of this system, we introduced some years ago a general theoretical description, which models the isotropic-nematic transition by properly taking into account molecular self-assembly, and we carefully verified the theoretical predictions against numerical simulations of patchy hard cylinders. Here, we provide a revised version of the theory in the attempt of understanding which assumptions are worth to be improved. In particular, we focus on the Parsons-Lee approximation and the modeling of orientational entropy. We compare the results from the revised version of the theory against original ones, showing that the present version of the theory is able to capture more accurately the phase boundaries of the isotropic-nematic transition. © 2019, © 2019 Informa UK Limited, trading as Taylor & Francis Group.