This is actually a question that involves both state (North Carolina) and federal issues, but the State issues are more of what I'm concerned with.

Long story short: for seven months (October 2011 to April 2012), I worked in France as an English teaching assistant. I filed returns (and all tax due) for the US both in 2011 and 2012, using the total gross income (as required) as the taxable base.

On all salaries, France imposes two separate taxes (contribution sociale généralisée and contribution à la remboursement de la dette sociale, or CSG and CRDS) that are withheld at source that, at the time, totaled about 7.86% of income. (CSG of 7.5% and CRDS of 0.5% applied against 98.25% of the tax base). By French law, these are income taxes (but not the income tax proper, impôt sur le revenu), and a memorandum of understanding was signed between France and the US in 2019 that says the IRS will not challenge tax credits claimed on the basis of the CSG and CRDS paid. Of course, I now can amend the returns to get money back (about $300 per year), because it's within the 10-year limitation period, but... the paperwork was from 8-9 years ago, and I've moved enough times to the point where I have no idea where the papers are anymore.

From a federal standpoint, it says all I would need is the annual withholding statement or some other proof showing how much total CSG and CRDS I paid. Is this really all I need to justify the amendment? (Also, which forms do I need to file? I'm guessing I'll need a 1040X, but they typically cover multiple years, and the 1116 for the year in question...)

From a state standpoint, North Carolina allows credits for foreign income taxes paid, including to another country. Thus, three questions:
  • If the tax is good for the Federal credit, will it be good for the North Carolina foreign credit (here, the CSG and CRDS)? This is one case where combing through statutes and regulations hasn't gotten me anywhere.
  • NC, at the time, normally required a copy of the return filed, but one does not file a return in France for CSG and CRDS. I'm assuming that a statement of withholding here should work too, correct?
  • It says that the NC statute of limitations for amendments is "generally" three years. Is the fact that I'm amending my Federal return(s) within the Federal statute of limitations good enough to allow me to amend the NC return for the credit? (This is also another $300-ish I could get back... not a lot, but with getting ready to move soon...)