Activation and transmutation simulations model the time evolution of a given nuclide inventory under various irradiation conditions. The results of such inventory simulations must be verified to give confidence in their predictions, with the reliability of these predictions dependent on the choice of nuclear data library. This work performs verification and validation of nuclear data libraries based on the fusion decay heat measurements performed at the Japanese FNS (Fusion Neutron Source) facility. Using the nuclear inventory code FISPACT-II, simulations have been performed with the latest official releases and test versions of TENDL, JEFF, and JENDL nuclear data libraries. The assessment compares the results between the nuclear data libraries themselves and benchmarks each against the experimental measurements, with example results presented for selected samples: barium, germanium, and chlorine. The high-fidelity simulations allow the contributions to the decay heat results from individual radionuclides to be studied. These results allow the quality of inventory predictions to be assessed for each library and indicates any inaccuracy/omission in the nuclear data, e.g., identification of missing production pathways and cross sections that need reviewing.