If I became a green card holder this year, could I amend my past tax returns since I was informed I didn’t get full tax credits due to my immigration status?

[Critter · Accepted solution]

The Protecting Americans from Tax Hikes or PATH Act made several changes to the tax law, including preventing retroactive claims of the EITC and CTC by amending a return or filing an original return for any earlier year in which the individual or anyone listed on the return did not have a SSN valid for employment. You can't claim EITC or CTC unless the Social Security number for you, your spouse (if married filing a joint return) or a qualifying child is issued before the due date of the return including any valid extensions.

http://www.thetaxadviser.com/newsletters/2016/jan/congress-makes-changes-to-popular-tax-credits.html