Evolution of COAL type systems of Table 1. For each system i.e. COAL-A (Fig. A) and COAL-B (Fig. B), the top and bottom panels on the left show masses and evolutionary stages of both the primary (WD) and the secondary stars during the nova phase when the mass-transfer rate () and surface chemistry (C/O, ¹²C/¹³C) for the donor (secondary) star evolve with time as depicted in the second and third panels. The right hand panels follow the post-nova merger properties i.e. mass, core-mass, luminosity, surface chemistry and its stage of evolution (EAGB/TPAGB). The COAL-A merger classifies as a J-star for the entire duration of its AGB lifetime, as compared to the the COAL-B merger that has C/O > 1 during TDU on the TPAGB resulting in a much shorter J-star phase marked by the vertical dotted lines.