Originally Posted by
n8-the-gr8
I'm not sure if United always displays PN space for one leg when not available across the full itinerary. I've seen it display PN4 for one flight and PN0 for another and other times I've seen PN0 for both legs even though one might display PN2 when searched along (the latter example I explicitly recall from booking international itineraries). So may just be an IT glitch that has progressively been fixed over time.
If it's a throughfare, UA will display the lowest number in each fare bucket,
e.g., PZ9 and PZ0 will show as PZ0 for both (but the PZ9 segment will clear at booking). If it's a broken fare (
e.g., a W and an S), UA will display the true numbers for each.