No data is passed to the success page... The data is passed to the pp_confirm.php page. You should save any database details on that page. You can use the bindings panel on that page to show you all of the values that are passed to it by paypal.
With express checkout your SESSION is maintained, so you don't have to pass the orderID or form reference to paypal, you can just save them in the session and they will still be available on the pp_confirm.php page.