It's not enough to adhere to the age signal:
> (3) (A) Except as provided in subparagraph (B), a developer shall treat a signal received pursuant to this title as the primary indicator of a user’s age range for purposes of determining the user’s age.
> (B) If a developer has internal clear and convincing information that a user’s age is different than the age indicated by a signal received pursuant to this title, the developer shall use that information as the primary indicator of the user’s age.
Developers are still burdened with additional liability if they have reason to believe users are underage, even if their age flag says otherwise.
The only way to mitigate this liability is to confirm your users are of age with facial and ID scans, that is why age verification systems are implemented that way: doing so minimizes liability for developers/providers and it's cheap.