Lifespan bias potentially alters species abundance in death assemblages through the overrepresentation of short-lived organisms compared to their long-lived counterparts. Although previous work found that lifespan bias did not contribute significantly to live-dead discordance in bivalve assemblages, lifespan bias better explained discordance in two groups: longer-lived bivalve species and species with known lifespans. More studies using local, rather than global, species-wide, lifespans and mortality rates would help to determine the prevalence of lifespan bias, especially for long-lived species with known lifespans. Here, we conducted a field study at two sites in North Carolina to assess potential lifespan bias between Mercenaria mercenaria and Chione elevata, two long-lived bivalve species that can be aged directly. We compared the ability of directly measured local lifespans to that of regional and global lifespans to predict live-dead discordance between these two species. The shorter-lived species (C. elevata) was overrepresented in the death assemblage compared to its live abundance, and local lifespan data largely predicted the amount of live-dead discordance; local lifespans predicted 43% to 88% of discordance. Furthermore, the global maximum lifespan for M. mercenaria resulted in substantial overpredictions of discordance (1.4 to 1.6 times the observed live-dead discordance). The results of this study suggest that lifespan bias should be considered as a factor affecting proportional abundances of species in death assemblages, and that using lifespan estimates appropriate to the study locality improves predictions of discordance based on lifespan compared to using global lifespan estimates.