This can occur if Password Settings Object (PSO) is applied, in this case the password lifetime is fetched from the attribute PasswordSettingsAttributeMaximumPwdAge otherwise its fetched from DomainAttributeMaxPwdAge.
Also :
- vCenter is using the default GPO to determine the Password expiration to display the notification instead. AD password expiry notification uses incorrect date for calculation.
- Microsoft Dynamic Access Control is used to set individual password expiration.