Neutral Beam Injection (NBI) is a flexible auxiliary heating method for tokamak plasmas, capable of being efficiently coupled to the various plasma configurations required in the Tritium and mixed DeuteriumTritium Experimental campaign (DTE2) on the JET device. High NBI power was required for high fusion yield and alpha particle studies and to provide mixed Deuterium-Tritium (D-T) fuelling in the plasma core, it was necessary to operate the JET NBI systems in both deuterium and tritium. Further, the pure tritium experiments performed required T NBI for high isotopic purity and reduced 14MeV neutron yield. For all of the experiments performed in the T and D-T phases an accurate calibration of the neutral beam power was required. Calculations of Q, plasma confinement, L-H power threshold and many other parameters rely on accurate measurement of the input power. In addition, the relative calibration of the power provided by D and T beams must be accurate to minimise uncertainties in the comparison of NBI heated plasmas used to study isotope effects. Accurate power calibrations are also essential to machine safety. Previously on JET there have been a number of questions raised on the NBI power calibration, in particular following the Trace Tritium Experiments (TTE). The NBI power is calibrated on JET using a combination of methods including the use of data from the NB Test Bed (NBTB) facility. As this facility cannot be run in tritium and the use of tritium is more heavily restricted there is more scope for uncertainty in the T NBI power calibration than D NBI. Operator activities on the tokamak NBI system, including calibrations, were performed in 2020. Following these activities, a series of plasma experiments were devised to further corroborate the T NBI power by comparing the plasma response to the D NBI power. A series of stationary, L-mode plasmas were performed on JET with different beam combinations used in different phases of the same pulse. By comparing the plasma response for D and T NBI it was possible to compare how accurate the T NBI power calibration was relative to the D NBI power. Measurements of the plasma stored energy (both steady and transient) and neutron rates will be presented together with results of TRANSP simulations of the relevant pulses.. The stored energy as measured by magnetic diagnostics, corrected for fast particle stored energy, show that the uncertainty in NBI power calibration in T is comparable to that in D.