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Good afternoon, Vinicius.
Thank you for sharing on the subject and in a way that is easy to understand.
A person who moved to the United States in 2014 and, due to a lack of knowledge, didn't file a final exit tax return, has been filing an income tax return every year.
In this case, it's possible to file a Declaration of Definitive Exit retroactively (which in this case I believe would be from 2016) and ask the IRS for a refund of the income tax overpaid, since in comparison to what he would pay as a resident abroad, it's lower than as a resident in Brazil.
Thank you in advance for your attention.