Probably the easiest way to tell is that you will have lost all of your user entered data except the data on the welcome page and the maps and other data that are stored on the card. If you made any changes in page sequences, page setups, etc., you will have to do all of those again. You also will have to re-enter stored waypoints.
Thanks for your quick reply. My data, waypoints etc is still there, so will have to try again.