After further research I think I may have discovered what triggers the abrupt switch back to original file names from the first card. I had a battery go down at just the same time that the file switched over, ie the file number was correct and continuous, my battery went dead and the file stopped and when I re-powered back up with the new battery that is when the files jumped back to the old numbers. I still don’t know why the camera did it but I know for sure that is where the jump backwards took place so you may have had some kind of similar power disruption with your shoot as well.