When to amend a rolling pro rata mistake?

Pro Rata rules kicked in for me in 2021due to backdoor Roth and owning a SIMPLE Ira; however, I was unaware until this year.

Also in 2020 I had an excess Roth contribution that was taxed/penalized for TY 2020 and TY 2021 until it was caught and back doored out of there in TY 2022. Do I amend the TY 2020 Form 8606 as if the conversion happened that year to create basis going forward for pro rata rules, or just figure them by hand for each year affected and then do one big balance for pro rata on the last tax return affected by pro rata which would be 2024?

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