OK, looking at the PSLibEnemy.java file I concluded that my missing Palma enemy is that big scorpion thingie. There are 27 .PALMA monsters (including the big scorpion from PSIV) and 27 spots on the list. I'm having that final ??? there because that enemy is not counted on the list. The same will count also for the the two other coloured scorpions. I also noticed some enemies that I haven't encountered yet, so there are a few yet left to find

If you could fix the scorpions, that would be great. No rush though, it's not a game breaking thing. To me it's just annoying as I like to explore everything and if there's a list that keeps track of all enemies, something in me compells me to find them all.
EDIT: Bugged in Undead is the Nightmare. According to the code it's an .UNDEAD (in the file named Saccubus). I defeated it, twice, but it doesn't show up under undead. My remaining ??? is an enemy that has eluded me so far so I will search for that

Under Special, the RobotCop does not show up, it should according to the java file.
Under Motavia I miss the Blue Dragon and the Barbrian (I encountered all three Motavian and the new one) and the big scorpion (and there's one foe I haven't encountered yet).
Under Dezoris I miss the Cyclops and the big scorpion.
So in short, most ??? on my list are foes I have encountered but are somehow not on the list (all the ones I listed above). I see them in the java file so they should be there.