I was a lucky recipient of 2 phantom upgrades (SEA-NRT and SFO-NRT) when the program ran. In the first case, I inquired at the gate about the possibility of an upgrade and was given a seat in WBC, and for SFO-NRT, I was running late for the flight and when my ticket was scanned at the gate the gate agent said "we've been paging you!", and handed me a ticket for WBC.

If I remember correctly, NW had some way internally of determining the worth of a customer, and that figured into how they determined who would get these phantom upgrades. At the time, I had only flown with NW for about 2 or 3 years at the time and was a platinum who almost always bought the cheapest fares possible.