@Opus 17
It looks like the payroll vendor made a mistake and paid me an extra paycheck in 2021. So this a slightly different than my original question where I assumed it was a 2020 error, but it's a 2021 error.
They are suggesting that I refund them the extra paycheck (gross) and they can send me a corrected W2 for 2021 which will show the corrected wages paid but will still show the additional taxes paid by me for the extra paid paycheck which I can then claim a refund for excess taxes paid (Fed, State and FICA) in my 2021 returns (due in April 2022). That sounds like a reasonable fix. Am I missing something?
