Man, why do we keep getting this question? And even from a veteran like vbt no less 🙁
There's nothing special with the disc itself. Nothing, zilch. The way the cd block works is once a disc has been verified as an audio cd, data cd(such as vcd, etc. Basically something other than a saturn disc), or an original saturn disc, it will unlock the drive. And it'll stay that way until the cd block is reset. All the system disc does is go through the normal process of disc authentication, and then allows the user to insert a different disc which it then boots.