Hi guys, not all banks use the issue numbers any more and so those who don't need it have replaced them with 0 and those that do carry on changing them .... so you are both right.
Now that the cards have chips in them the bank can tell as soon as they are swiped which card it is, but back when it was just the magnetic strip the issue number was required.
this helped if you lost the card, a new card would be issued and could be used straight away as the issue number had to be typed in when you used it in a store (so that they would not decline the wrong card). Some banks chose to delay the new card being released by a few days instead ( hence no number any more) as cards that are stolen only tend to be used for the first 48 hrs after that the majority are discarded. Some banks such as the Halifax still use the issue number as they find it helps clients remember which card is the right one to use!!!!