How often does a health plan discover that an enrollee is not the participant’s child?

Some employers and administrators use a dependent eligibility verification to find people not eligible for coverage under a health plan.

These find participants who enrolled as a spouse someone who was not the participant’s spouse.

But how often does this find participants who enrolled as one’s child someone who was not the participant’s child?

BenefitsLink neighbors, any experiences you can describe (with anonymity)?