IndoorCam P24 Reading old .DAT files

I understand that the dat files are encrypted and that the app is the only way to read and download them. The scenario is that I have used one sdcard that was 2GB and then upgraded to a 16GB. I went to move my old.dat files over to the new card but when I do that all history of old videos are now gone. The dat files are still there. New dat files appear to be created and show in the app okay. Is there anyway to have the app ready the old dat files?

Any ideas?