I was "adjudicated" (not "Convicted") as a "Youthful Offender" relating to an arrest for marijuana possession, before I was 18 years old. After passing an FBI background check, while I was imprisoned, I was paroled and began service in VISTA-a federal program now part of the Corporation for National and Community Service.
A few years later, while a candidate for public office, I was asked by a newspaper reporter about my criminal record. I had been told my "youthful offender adjudication" had been "sealed", so I didn't confirm it at that time.
About ten years later, while working as an Armed Airport Public Safety (Aviation Law Enforcement & Crash-Fire-Rescue) Officer, my Armed certification process required an NCIC (National Criminal Information Center) check by the State Police in my state of residence [at that time]. The computer check noted: "Paroled...to [city/state] for one year and three months // Sentenced under the Youth Corrections Act-Do Not Publicly Disclose this information". I contacted an attorney in my former home state who wrote the State Police Armed Licensing officer in my current state of residence-noting I had been "adjudicated [not "convicted"]...and I was subsequently able to be certified to be "Armed". The Attorney in my former state of residence checked the local County Clerk's office, to review my file, and he discovered that not only was my record not properly sealed, neither were about 200 other "Youthful Offender" records in just that county alone. He took the matter to the County Court, and the Judge ruled the County Clerk had to properly seal all of those so noted, and that fingerprints and "mug shot" photographs be destroyed, and that computerized records with that state's system be corrected.
Some years later while completing training to be a Foster Parent, my "background check" came back with no adverse information.
I hope this presents an overview of some of the potential problems one might encounter with "Background checks" in an assortment of situations and communities.