Short answer
A UAN is a 12-digit number the EPFO gives each employee. It stays the same across jobs and links every PF account the person has.
In AdviHR
AdviHR validates the UAN on the employee profile and lists anyone missing it before you generate the ECR.
12.
How sure are we? These figures use the same rules AdviHR payroll applies. We publish what has been checked against an official source and what has not, on the statutory accuracy page.
General information, not legal or tax advice. Confirm against the official notification and your adviser.