@yon2655 below is my view on this ---
First the situation --- Person A uses somebody else's SSN, is without papers and works in the USA ---- SSN is SSN#1. Subsequently A receives work permit and gets a proper SSN called SSN#2.
IRS does not care whether the earner is legal or illegal with or without work permit. All they care about is that each earner has paid the proper taxes ( including Social Security and Medicare ). Thus the easiest solution is for this person A to have two W-2 issued --- one with the original (fake? ) SSN#1 and a second with new issued SSN#2. This does mean help from the employer and also means that the FICA contributions would go to two SSNs ( SSN#1 and SSN#2 ) and the Person A when retired would only get the benefits based on payments to SSN#2. Everything depends on how the W-2 is issued.
Does this help ?
