Mostly a curiosity, no real complaints or issues here. DL 937 LAX-CUN on 12/15/14. No Business seats, in any fare bucket, from about 3 weeks out up until 1 hr to departure (checked detla.com, called DM line, all the same: "sold out in J, not a single seat available" for cash, miles, ... bullion). Yet there were 9 unoccupied seats out of 16 on the seat map, also up until the departure (seat map is not a perfect indicator, I agree, but still a decent guide). Over 40 seats open in Y.

After checking in, the UG list showed 9 seats available in J, 39 in Y. Obviously, an easy upgrade. 7 seats in J went empty. About 25-30 in Y.

Not a big deal - except 5 people in my party did not want to take the risk, bought J tickets on UA. At about $2,200 a piece, DL just lost $11K in revenue for a 4-hr flight that would be a good profit for them (an older, seen-better-days 737; not really an international J, could not cost them that much to operate). What gives? Delta literally would not sell tickets even at LAX, 2 hrs before departure - the seats were clearly there. Software bugs, something else?