well, with disk based games, i believe that the only point of checksum validating an iso is if the targeting patch actually requires a checksum match to function (xdelta throws a fit if you try to patch an xdelta file to an iso that has a different checksum than it was intended for) but as with optical image isos the checksums might and oftentimes do differ while the game data itself might still be just fine. Especially in the case of PSP where rippung the UPDATE folder out from the iso to save space is extremely common. But since people in general use patches such as ips, bps or xdelta for games, a checksum matching .iso is required.
like earlier was mentioned, especially ps1 and ps2 tend to reuse their game ID between versions of the game and oftentimes identifying what is what can get really tricky. For an example, there is 3 revisions of japanese valkyrie profile for ps1, and aside from the size of the data container (which is compressed and encrypted.) their contents are, to my knowledge identical.
Telling them apart is virtually impossible if you dont know what you're looking for, such as internal file build dates or specific filesizes.
it really boils down on how the game and it's data is intended to be used.
It is for this reason alone I'm personally shifting away from using "patch" files in general completely (I only work with systems using optical disk media), and the hacks I'm doing nowadays will eventually be released as pure assembly code and resource assets (graphics, video, audio) instead. Providing a copy or a download link to Kingcom's armips to assemble the code and a tool for rebuilding both the .iso file and the relevant data containers will do the job regardless of if the game's checksum matches anything, as long as the data itself is not damaged.
I haven't gotten to the point of releasing anything yet, but Im hoping that once my little project of translating zill o'll for psp is complete, i will along with the patch, provide a solid enough patching framework (commandline .iso tools, amongst other things.) that maybe perhaps in my ideal little world, people adapt to use, making this whole checksum-specific .iso files thing obsolete.
i do see the good thing in having such a validation for checking, for example the SLUS code of a playstation *** game, which can quickly identify if you have a PAL/US version of the disk for example, but beyond that there is little use for it what comes to identifying a suitable iso for a specific patch, because as already said, a lot of patches simply require a matching checksum, so any further validation is instantly rendered pointless.