To my knowledge, there is nothing in writing about what is a material error that requires correction or how far back you should go. I encourage you to contact FinCEN's Helpline @ 800.949.2732.
Anticipate that they will ask you how far back this goes and how many corrections might be involved. (This is not a backfiling determination; these forms were already filed.)
Make a note of the date, time, & who you spoke with and follow the advice. Write a memo to file explaining the situation, how you found it and what training steps you have taken to make certain it does not happen again. (Examiners will see the corrections, have your explanation ready.)
In this world you must be oh so smart or oh so pleasant. Well, for years I was smart. I recommend pleasant.