I've read that some PS2 firmware binaries relating to PS1 backwards compatibility/emulation contain lists of games (e.g. serials). I think this is worth investigating as a potentially useful source for the PS1 undumped lists. I think it'd be worth at least ruling out the possibility (in all dumped versions of the PS2 BIOS).
Non-exhaustive list of relevant links:
https://playstationdev.wiki/ps2devwiki/ … OP/Deckard
https://github.com/wisi-w/DKWDRV
https://github.com/wisi-w/DKWDRV/blob/main/tech_docs.md
https://www.ps2-home.com/forum/viewtopic.php?t=7968
https://psi-rockin.github.io/ps2tek/#bi … patibility