It was my understanding that Delta was very protective of this new PS product and would not allow upgrades. I flew DL 120 from HND to MSP today. 90 min before the flight there were 24 seats showing in PS per the app. 100+ seats open in coach.

When I boarded the plane every last PS seat was taken. Surely these were not OP ups since coach was about half full. Where did these people come from at the last minute?