Probability distributions of the difference between the system masses measured dynamically and those derived from evolutionary models using component luminosities and system gyrochronology ages for the brown dwarf binaries Gl 417BC (violet) and HD 130948BC (blue). Multiplying these two distributions gives the joint constraint (black). For both systems, the directly measured masses are systematically lower than predicted by all three models. This is an alternative way of viewing the same discrepancy shown in Figure 3, caused by model-predicted luminosities that are too low at this mass (≈45–60 M_Jup) and age (≈800 Myr).