The 1444 letter was for the first stimulus payment ... the 1444 B was for the second stimulus payment and the 1444 C is for the third stimulus payment.
The first 2 stimulus payments are reconciled on the 2020 return and the third on the 2021 return. If you got a notice that a payment was sent and you did not receive it then you cannot apply for it on the 2020 return instead you must put a trace on the payment. If you put it on the 2020 return then expect the IRS to correct this "math error" and adjust the bottom line of the form 1040 accordingly.
