Originally Posted by DMPHL

It's possible that all of them were upgrades, but I wouldn't say it's necessarily likely that they were. After that, even if they were upgrades, that doesn't mean that the available seats would be released to C inventory for SWU. They may have been purchased with cash, or may have been available to book with miles.

What route are you flying? If it's any of the South American routes that uses the 77W (DFW-GRU, JFK-GRU, MIA-GRU, MIA-EZE), I'd be surprised these days for an EXP not to clear a SWU, but still possible. If it's DFW/LAX/JFK/MIA-LHR, it's entirely possible that those seats are all purchased, or that only a couple SWUs clear, and that J and F tickets get purchased close in. Same with DFW-HKG. LAX-HKG should be easier, but depends on the day of the week/season/is still unpredictable.