Whoever said there were 16 permanent slots and not 19, I think you for not including mark/weapon/shield instead of just being wrong.
Those three special goit slots are treated as if they don't exist. The ability is supposed to destroy perms in the final two permanent slots/last three creature spots. Correcting.
Being moved two slots back means being moved from slot 1 to slot 3, from 2 to 5, etc. Yes. It looks extremely crazy in practice.
Blame Zanz being silly.