The August 31 date was from an IRS release from 2020.
This is from Form 8915 instructions.
Line 14. Enter on line 14 of your 2021 Form 8915-F (2020 disasters) your total repayments—the sum of your excess repayments carried to 2021 and your repayments made for 2021. See Worksheet 3, later. A repayment is made in 2021 if it is made before you filed your 2021 return, and not later than than the due date (including extensions).
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