RVL_DIAG is a factory disc with ID 100J (0000). It is interesting because it does not seem to be hash checked.
RVL_DIAG has a single content with type
0x2 and hash
934db10dacfe4f410d83e8e6456767b68bd91a7a (4 bytes), which turns out to be
0xCAFEDEAD in the opposite byte order).
Because the real disc has been seen, and it has a real UI,
0xCAFEDEAD is clearly not the actual disc. It is therefore probably the case that this content does not receive any form of verification.
The only code in IOS to disable signature checks is for the disc header, which means that was how signature checking was disabled. The content type is not read by DI or ES.