Monstrous Hit Dice

I’d never realised how radically different Basic/Expert Dungeons & Dragons is from Advanced Dungeons & Dragons until I started flipping through the Old-School Essentials Monsters book. I was struck by a simple fact that has been gnawing away at me ever since: the Giant Roc has more than three times the Hit Dice of the most powerful Dragon, the Gold Dragon.

The OSE entry for the Dragon states that:

Older dragons may have up to 3 HD more and twice as much treasure.

Old-School Essentials, Classic Fantasy Monsters, page 16

So that would boost the Gold Dragon to 14HD – still less than half the Hit Dice of the Roc. I was, frankly, dumb-founded. Maybe this was an (unlikely) error on the part of OSE? Checking the Basic D&D Rulebook (1981), we read:

Dragons generally range in size from 3 hit dice smaller to 3 hit dice larger than average…