I agree it is a ridiculous criticism (in the context of so much else that is wrong), but NW's system did have some nice features. For example, if it was a four digit flight number starting with a 2 you knew it was a CRJ with no first class. And usually the outbound flight from a hub differed by one number from the return flight. It offered a poor man's way of doing the "Where is my flight coming from" that is one of the great features that CO offers on its web site.