For 2-b, 3-b and 4-b interactions included in q-AQUA and q-AQUA-pol, these are respectively the dimer, trimer and tetramer. CCSD(T) calculations are quite feasible for these and so a large range of geometries and energies can be explored for them. PIP fitting for the dimer and trimer was certainly feasible a decade ago as these were just 6 and 9-atom systems. The tetramer was a challenge a decade ago as it is a 12-atom system; however, given the recent progress in doing PIP fitting, the fit for the 4-b became quite feasible. In any case, one consequence of training on these small clusters is the high accuracy in describing the energies of other clusters such as the hexamer, provided the MB representation up to the 4-b is accurate for these clusters. Indeed that was verified even for clusters as large as the 20-mer and also for clusters up to the 25-mer. The question that if a 1-4 body MBE would also provide an accurate description of condensed phase water, as demonstrated by q-AQUA, was certainly not obvious; however, as we showed elsewhere 10 and here for the order parameter it is. In one respect, however, we were not satisfied with accuracy of q-AQUA for the density. By interfacing q-AQUA to TTM3 we have "hedged our bets" and hopefully provided a somewhat more solid footing for q-AQUA. By contrast, training for the atom-centered NN force fields is done on samples of ca 32 or 64 monomers from direct DFT-MD simulations. Transfer learning is then done on even smaller samples using approximate but feasible CCSD(T) calculations. So, it would be interesting to see if these NN-TL force fields produced the level of accuracy seen here or in MB-pol for the hexamer isomer energies. These were not reported in the two recent NN-TL force fields, and so we are only making an educated speculation here.