Hi Claudia, I will give my opinion, but like everybody said do not take it as a fact, consult with a specialist in taxes.

If your client had a C Corporation, the $12,000 deposited in year 2021, had to be declared the whole amount in 2021 on the C Corporation tax.  I really think that should be done the correct way and  go back and issue or correct  941's of 2021, pay the withholding amounts from the salary  and issued the w-2 for the whole amount of $12,000 for year 2021( because my understanding is your client works for that money, so social sec and medicare as well as taxes should be withholding). It does not matter the year, or the way that you client  withdraw the money, the fact is that the whole amount are commissions (revenue) and  were earned in 2021, and should be declared and pay the taxes on 2021.

Also, it does not matter,  if your client  lend the money to the Corp before, the entries are revenue and needs to be declared as earnings and pay taxes. Good luck!