This is completely untrue. United have spent the past year and more trying to
persuade me and many others to add a PIN to our accounts instead of/in addition to a password, just because pre-merger Continental customers had them. We have steadfastly refused to do so on security grounds. We have never had PINs and will not agree to invent them. My pre-merger United 2-digit 6-letter password is infinitely better security than any 4-digit PIN.
If you say so. It's the same IT system. My money is on you having one, whether you added one or not.