"All of these cases had priority dates before 2007, so clearly, they were upgrades. For example, 363 of the 2,800 EB-2 cases from India that were approved in March 2012, had a 2005 priority date."
Q, I think the only way they can tell if it was an upgrade is to ensure that the PD was prior to 2007. Otherwise there is no way to tell if it was an upgrade unless the GC is actually issued and the related case taken off of USIS' inventory.
EDIT: I do feel that 15K is huge and improbable. Given the hoops people have to jump through to pull off the upgrade in a tough economy. However if this is true, we have a loooooooooong wait coming up.