In this particular case the FTC limit for each year has never been exceeded because the foreign taxes paid have never been entered on form 1116 under the general category on any return. No allowable portion of the FTCs were ever used. The FTC is related to taxes paid on wages above the Foreign Earned Income Exclusion (FEIE) and fairly easy to calculate by multiplying the foreign tax paid by the ratio of the FEIE / Total Foreign Wages to find the disallowed portion of the foreign tax and then subtracting this from the total foreign tax paid to find the FTC.
With the 10 year carry forward limit, carrying forward the calculated unused FTCs starting with 2012 seems to be the only option. The total FTCs from 2012 forward will fit under the combined FTC limits of 2020 and 2021. Therefore amending the 2020 and 2021 returns for refunds will capture the unused FTCs going back to at least 2012. All FTC before that date are lost.
