For your 1969-S Cent what you have is contact damage to the lower part of the "O" as well as a minor die chip inside the "O" as others have already noted [see attached marked pic of you're coin].
The die chip is not a dropped letter error. You can check out this error-ref.com page for dropped letter errors here ... https://www.error-ref.com/struck-through_dropped_filling/. Also, see this error-ref.com page for die chips ... https://www.error-ref.com/die-chips/#:~:text=Definition%3A A small piece (less,lump in the affected area.
I understand your desire to document the die chip error, but it is a very minor and common error, and really doesn't add any value to the coin. It would be about $100 to submit the coin to NGC, and they would just grade it and put it in a holder. If you want to keep it, I would just put it in your own holder or flip and label it as AU-58BN as Sandon noted, and add "Minor Die Chip".