I think the key is in that sentence. What probably happened, IMO, is that his date of purchase was what got him to be #1 on the list. He was probably also already in the upgrade queue starting 5 days ago instead of your 4, so there may be a slight "penalty" to buying a non-full fare ticket less than 5 days out for a Platinum. I'm theorizing here, but part of the reason the "date of purchase" criteria is present may be because NW likes to know if they're going to have revenue as early as possible. In this case 5 days out instead of 4, so perhaps they give him priority? And because of this, perhaps in the window of less than 5 days out, fare class matters less than purchase date?