Not sure why some of your old waypoints would be dated the same, but the waypoints you marked when using the Simulator mode (forced or automatic) would take on the date from the simulated GPS Receiver which must be June 14, 2008.
Not simple but you can change the dates to the current date by using HumminbirdPC to make a duplicate of the waypoint, deleting the original and renaming the duplicate one (it will have the same name plus (01) or (02),... behind the original name. You could also delete the original waypoints and type them into HumminbirdPC again.