Fyi, normally delta does not open up more G/Z inventory on day of departure for domestic flights... it goes to V/X complimentary medallion upgrade inventory. From your description of the upgrade list, it actually sounds like your group was put in order according to medallion status. The miles had nothing to do with it.

The medallion gate upgrade priority list doesn't have a slot for mileage upgrades making a difference... and for SWUs the agent had to put the proper text in your PNR for the system to recognize it and give you higher priority, which I recently found out was not done correctly on one of my flights and I ended up sitting in back on JFK-SFO when I would've cleared if my SWU was processed correctly.