Either the information should be stolen from Coruscant while the Death Star and Endor are far away, or else they shouldn't have to steal anything but a glance of the Death Star from a ship near Coruscant. It would seem kind of silly to sneak onto Coruscant to steal information about the Death Star that can be seen hanging there in the sky. If we were to make such a scene, I think it would be best to keep the Death Star away from the general populace (it is a secret construction project after all) while the Rebel spies managed to steal the info from Coruscant.