Actually that's a good, accurate description. To make it simpler - the knee of the head is the flat plastic piece that sticks out from the forward end of the hull. (On the kit it's cast integrally with the hull.) It winds up under the bowsprit, and the figurehead is mounted on the end of it.
To see the mistake that Revell made, you'll have to have a copy of the plans of the ship. A good way to get them is to get John McKay's Anatomy of the Ship: The Armed Merchant Vessel Bounty. (I may have garbled the title slightly.) In addition to Mr. McKay's own superb drawings, it contains photos of the Admiralty draughts.
If you compare the side view ("outboard profile") of the plans with the Revell kit, you'll see the difference immediately. There's supposed to be a subtle S-curve to the forward edge of the knee of the head (that "handsome serpentine line or inflected curve" in the definition above) that Revell just plain botched. I have no idea why that happened.
As I remember, I cut my replacement knee of the head out of either .060" or .040" styrene sheet, and scribed the edges of the various component pieces on it to match the "planks" I'd scribed on the hull halves. (As I said in the first post in this thread, I'm not at all sure that using the plastic hull saved me any significant amount of time.)
Replacing the knee of the head wasn't a huge job. But if you leave it as is, I don't think anybody will mind. I certainly won't.
Hope that helps a little.
Youth, talent, hard work, and enthusiasm are no match for old age and treachery.