Why an N3 follow-on would not simply add twelve 16.5-inch guns

Would the Royal Navy follow N3 with a twelve-gun 16.5-inch battleship?

Probably not; a follow-on would likely move away from the unfinished N3 layout toward a faster, more mature capital-ship design.

The Royal Navy might eventually adopt 16.5-inch guns in this counterfactual, but a straightforward twelve-gun repeat of N3 is considered unlikely. A successor would probably move toward a fast battleship, whereas N3 was not one. The familiar N3 design was unfinished and would have required further changes before construction. G3 had priority because the Navy considered its shortage of useful battlecruisers more pressing. The later suggestion is to raise the roughly 25-knot design's speed by enlarging the hull and installing more machinery. That would be a brute-force solution, and the precise final design remains speculative.