16GB CF card lost my images?

Hey guys

I have a bit of a dilemma. Today I went out to shoot a wedding, same as usual put in one of my 16gb cards, formatted it, and proceeded to shoot close to 600 images before swapping it out for a new one. I did this through out the day as usual, formatting the new card as usual. However, when I went to load the images to my computer, one of the cards (the first one I used) was displaying images a shot the previous wedding, BEFORE I formatted the card.

Now, before I the formatted the card, it was completely full. Therefore the possibility of me forgetting to format it before shooting is not possible because, like I said, I proceeded to shoot 600+ images. Everything was working as normal, everytime I took a shot it would preview on the LCD and I could review through previous images. But then once plugged to computer these new images are nowhere to be found, it’s just showing the images prior to formatting.

I’m currently running the card through recovery software, crossing my fingers that it recovers the images I shot. But does anyone have any idea why something like this would happen? I’ve had cards corrupt before but nothing like this. Any input would be much appreciated. Thanks!