You stated this "After both happened, I still had a 210 day lockup period which ended on 12/10/20. My company set the taxable amount on my shares at close of market on 12/9/2020 when the stock price was $47 per share"
What you said there is that the shares were granted but NOT vested until end of day 12/9/2020 This is the very definition of an RSU. The share price at the end of the day on 12/9/2020 (vesting date) is what the FMV of the shares "at vesting" was. This is one of the really ugly facts about RSU grants. At the instant they vest, you are taxed on the value as income. So, your W2 is correct. This is the way the system works. The fact that the stock price dropped while the "sell to cover" action was taking place is irrelevant to your W2 income as is the fact that the remaining shares were not "released" to you until after the sell-to-cover action had completed.
This has happened to me 2 years in a row now. Last year it took 2 separate sales to cover, and this year it took 3 because the stock dropped. In addition, my shares vested during a blackout period, so I couldn't transact any of them EXCEPT for the sell-to-cover action.
This year at least, for me, ETrade had a better supplement which had all the corrected cost basis values for each separate sale. So, as MANY people have said here, you just enter the sales as "non employee" stock and adjust the cost basis per the supplement. And, as a check, if you have an amount reported in box 14 on your W2, that should equal the cost basis on the supplement...that's how you know what portion was reported as income.
