You can only go back three years to amend a return to receive a refund, but if you owe taxes you can go back further. So, you would only amend beyond the previous three years to report taxes you owe.
You can submit the amended returns at the same time. You can bundle supporting files as long as you make it clear to the individual processing the amended returns what you are doing.
You should complete your current Form 8606 correctly, reflecting the changes you made to the ones from previous years.
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