Norm Deets II
Maybe since it's an expansion it's assumed you'll use those in the main box.
I'm almost certain that is correct. Since GH is an expansion, albeit a big one (especially KS edition), I believe you are meant to use the original 6 that came with the core game. This would be similar to Kaiju Rising and Jurassic Perils, both of which came with new characters and their associated cardboard standee, but no base. I think the only reason it feels odd is because GH came in a full size box, so it somehow feels more like a full game (although you still need, at minimum, scavenge decks and tiles from the core in order to play).
BTW - my wife and son have enjoyed the expansion so much we have already completed the 4 classic monster scenarios. We felt the 1st and 4th were the hardest, probably because they required scavenging. We only won #4 by 2 party members sacrificing themselves to kill off the last 2 bosses while the 3rd boogied back to the already refueled van for the win - with 4 health points remaining! ;-)