I believe you are on the right track with the completion of FOA, but I think what you are saying is more geared towards misedemeanor crimes. Even completed FOA for FELONY charges will show up on a criminal justice run RAP SHEET. They never go away unless expunged.
And as far as Juvenile records, if you are charged as a juvenile with misdemanor crimes people will never know. If you are charged with a felony as a juvenile your criminal history begins.
When you get arrested and fingerprinted you will be issued a finger print ID number by the state and feds. So if you get arrested as an adult and were charged with a felony as a juvenile, when your criminal history is run those state & fed issued numbers show up, and thats how law enforcement knows you were a delinquent. And if you are charged as adult, while a juvenile it will not go away. Your criminal record will be handled as an adults.
I went to my police HQ and ran a criminal background, it was a "RAP" sheet that was shown to me. I did it twice, once when I didn't get my background updated which showed the FOA, the second time was when I contacted GCIC to update my background and surely the rap sheet came back as "No record"