2019 = meaningless now; that was for Advance payments. Tax filing 2020 is all that matters for EIP 1 and 2. The IRS guesstimated on 2019 or 2018 tax info, which is all they had on file at that point.

And the payout for EIP 3 is driven by what the IRS already knows. If there is no tax return filed and processed already for 2020, there is only 2019 to base it on.