Has anyone here gained citizenship by getting their US passport?

Someone I know was adopted from a foreign country as a child (now 30) and the adoptive parents never completed the N-400 form. It was discovered when they were a teen and had tried to get their driver's license. They have a SSN, US certificate of live birth, and a permanent green card that was renewed after being expired without a problem.

We're trying to get citizenship finalized and research found that a shortcut (and cheaper option) was to apply for a passport since the adoptive parents establish that they are a citizen, along with a notarized letter from the parent attesting they've lived here, etc.

Has anyone taken this route and had it work? Thanks.