The barcode isn't what the Playstation 2's drive Mechanics Controller (MECHACON) checks for.
Originally Posted by maverick5992
It tries to read a code that's in the inner-most track of the disc that is out of range of most CD/DVD readers.
That's why people have developed mod chips - to trick the MECHACON that the track/code that it tries to read actually exists and is correct.
And for your own information - the console doesn't perform a disc check whenever an ELF is executed.
If your swap trick fails, then it means that either your game isn't a good candidate for the swap trick, the disc you are trying to swap to isn't readable by the PS2, and/or you swapped the discs at the wrong time or was not fast enough.
Unmodified SCPH-77006 with SM 3.6
SCPH-39006 with M-chip modchip, SCPH-10281 NA and refurb Seagate 80GB HDD
SCPH-10000 v1.00 with SCPH-10190 PCMCIA NA and SCPH-20400 HDD unit