Apparently, it was from the deductible portion (maybe 80%) of the federal ES#4 for 2020 made in mid-January of 2021. So it is not the pre-payment itself, per se. (And the fact that the dollar amounts did not align -- deduction carryover did not equal the ES payment -- made it hard to identify the origin.) At least this is how my accountant (eventually) explained it. I do not need it for 2021 tax year and it will not carry forward any further so I guess I can just ignore it.
