A glass is not in thermodynamic equilibrium below its glass transition temperature (Tg), and consequently, its properties, such as enthalpy, volume, and mechanical properties, evolve toward equilibrium in a process known as structural recovery or physical aging. Several recent studies have suggested that the extrapolated liquid line is not reached even when properties have ceased to evolve. In this work, we present measurements of the enthalpy recovery of polystyrene at an aging temperature 15 C below the nominal Tg, for aging times up to 1 year. The results indicate that the equilibrium liquid enthalpy line can indeed be reached for aging 15 K below Tg. The results are analyzed in the context of the TNM model of structural recovery.