Problem solved! Because SDXC cards are intended for sizes all the way up to 2 TB, the FAT (exFAT in this case) is different from SDHC cards. This means that the SDXC card is often not compatible with OS's prior to Windows 7. I was using XP at home and decided to bring the camera into the office to give it a try. Sure enough, using Windows 7, all of the files were there on the card in the usual place. What a HUGE sense of relief!
Thanks everyone for the help! Very much appreciated. Hope my brush with incompatibility helps someone else in the future who might encounter the same thing.