In the paper we present an overview of interpretive modelling of a database of JET-ILW 2021 D-T discharges using the TRANSP code. Our main aim is to assess our capability of computationally reproducing the fusion performance of various D-T plasma scenarios using different external heating and D-T mixtures, and understand the performance driving mechanisms. We find that interpretive simulations confirm a general exponential relationship between increasing external heating power and fusion output, which is supported by absolutely calibrated neutron yield measurements. Comparing measured and computed D-T neutron rates we find a strong dependency of the discrepancy between the two and absolute neutron rate. The calculations are found to agree well with measurements for higher performing discharges with external heating power above ~ 20 MW, while low-neutron shots display an average discrepancy of around + 40 %. A similar trend is found for the ratio between thermal and beam-target fusion, where larger discrepancies are in average seen in shots with beam-driven performance. We compare the observations to studies of JET-ILW D discharges, to find that in average the fusion performance is well modelled over a range of heating power, although an increased unsystematic deviation for lower-performing shots is observed. The ratio between beam-induced and thermal D-T ion fusion is found to be increasing with a weak exponential dependency, with the maximum achieved value of > 1 in a baseline experiment. An assessment of the fusion power computational uncertainty due to uncertainty in the input data shows a strong dependency on the plasma scenario due to the sensitivity to performance drive mechanisms, varying between +/- 25 – 35 %. Alpha particle simulations have shown that the ratio between volume-integrated electron and ion heating from alphas is < 10 for the majority of discharges, with alpha electron heating power reaching a maximum of ~ 70 % with respect to that provided by combined beam and RF injection in the core. An alternative workflow was needed to correctly model the DTE2 shots with highest fusion yield because of the use of fundamental majority RF heating, which was calculated to have provided ~ 10 % to the total fusion power.