Sorry for the confusion with this. This is expected and the MOD16A2 V061 will not be processed earlier then 2021. Following is per the MODIS Science team:
Before the start of V61 processing it was decided that the regular MxD16A2 and MxD17A2H will be only produced from forward processing but it will be the gap-filled versions MxD16A2GF and MxD17A2HGF that will be processed over the entire mission period. So since we had started the C61 forward processing from 2021 onward, the regular MxD16A2 shows up from 2021 onward. This was done in consultation with the science team as everyone felt that in the longer term the gap-filled ones are more accurate and useful so the regular versions are just temporary place-holders, to be eventually replaced by the gap-filled products.
Please let me know if youE have any questions.