I ended up using an online save editor to just edit the save and get a 9th keycard to open the last door, and also to get the shotgun, and also to unlock level 3 again since level 3 has that hidden scene that's not present in the gallery as far as I can tell.
I also read that supposedly the Konami Code ( ↑ ↑ ↓ ↓ ← → ← → ? ? Start?) works for unlocking all the data core doors, though maybe that was just in the demo? I couldn't get it to work anyway, but not sure what the B, A inputs would be in this case.