That's not how it works AFAIU. The bios only boot the game it the CD-ROM controller "tells" him the disc is a SaturnDisc. PseudoSaturn boots the disc even if it's not a saturn disc as long as the header is PseudoSaturn (So only game disc are booted, not VCD and audio discs). For a fix, when a non-saturn disc is detected the bios would need to check if the header is PseudoSaturn then boot if so. Now, you might be right if the CD-ROM controller passes the header to the bios, but I doubt that's how it works. IMO it's a flag bit/byte/WORD.