It depends.
For the FBAR - 6 years filed on BSA E-Filing System
For FATCA - Summary of FATCA reporting for U.S taxpayers gives the requirements for filing. You may need to file up to 6 years of returns. You could potentially get by with just 3 years of amended returns. If you really just didn't know better, 3 years of amended returns should be sufficient. If you file 6 years, you are shielded from criminal prosecution.
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