The purpose of UAN is not facilitating background verification possible but to have a unique identification to a member which can be used whenever he changes employment. Obviously, using the UAN of the person who joins your organisation you can understand his date of joining the previous employment but the objective of the back ground verification like whether the employee was good at his work?, whether the employee was fired for any misconduct? whether the previous employer would take him back if he goes back to him? etc which are more important than the date of joining his previous employer or the salary declared by him (that anyway cannot be checked because the PF records only show the PF qualifying wages and not the gross salary or CTC!!),cannot be verified using UAN.