Do you know what an audit is? Have you ever worked somewhere with record keeping requirements? At a financial company I worked at, we recorded every customer interaction and every decision made for accounts (including "nothing to do now") along with the inputs to those decisions. Auditors would ask to see details of random accounts to show we were keeping those records. Your grocery store or liquor store aren't getting their shipments and sales audited for id checks. You can tell because they don't always card you if you look old enough, or might accept being flashed an id. The way the law is enforced in person is that an underage person buys something they're not allowed to as part of a sting. You get in trouble for actually providing service to a minor.

Like I said, I've seen no laws requiring any audits or record keeping, and actually every law I've seen explicitly makes such records illegal.